BALDOCK, Circuit Judge.

In the 1990s, federal prosecutors handling large numbers of illegal re-entry and other immigration offenses developed early disposition or "fast-track" programs in states along the United States border with Mexico. In 2003, Congress endorsed such programs, apparently for border districts and elsewhere, in a broadly-worded provision of the Prosecutorial Remedies and Other Tools to End the Exploitation of Children Today Act ("PROTECT Act"). Pub.L. No. 108-21, 117 Stat. 650 (2003). Congress specifically instructed the United States Sentencing Commission to promulgate "a policy statement authorizing a downward departure of not more than 4 levels if the Government files a motion for such departure pursuant to an early disposition program authorized by the Attorney General and the United States Attorney." Pub.L. No. 108-21, § 401(m), 117 Stat. at 675. In response, the Sentencing Commission promulgated U.S.S.G. § 5K3.1: "Upon motion of the Government, the court may depart downward not more than 4 levels pursuant to an early disposition program authorized by the [Attorney General] and the United States Attorney for the district in which the court resides."

This sentencing appeal presents us with two questions related to the presence of fast-track programs in some federal districts, but not others. The first question is whether a sentencing court in a non-fast-track district has the discretion to consider sentence disparities caused by the existence of fast-track programs in other districts, and, based thereon, vary from the applicable guideline range for a defendant charged with an immigration offense. If so, the second issue is whether the apparently nebulous eligibility requirements for fast-track programs relieve a defendant charged with an immigration offense in a non-fast-track district of the burden of showing entitlement, at least in some sense, to sentencing consistent with a fast-track program. We hold that (1) where the circumstances warrant, a district court in a non-fast-track district has the discretion to vary from a defendant's applicable guideline range based on fast-track sentence disparities, but (2) a defendant bears the initial burden of showing entitlement, in some sense, to a variance based on fast-track sentence disparities. Given the facts presented here, however, we need not now decide the precise extent of a defendant's burden.

I.

Following a routine traffic stop, Colorado law enforcement officials arrested Defendant Martin Lopez-Macias, a citizen of Mexico, on suspicion of marijuana trafficking. Immigration and Customs Enforcement officials interviewed Defendant while he was in Colorado custody and determined his illegal status. A federal grand jury subsequently indicted Defendant in the District of Colorado for illegal reentry into the United States after deportation following an aggravated felony conviction, in violation of 8 U.S.C. § 1326(a) and (b)(2). In 1993, a California state court convicted Defendant for selling a controlled substance, heroin, which qualifies as an aggravated felony pursuant to 8 U.S.C. § 1101(43).

Defendant and the Government entered into a plea agreement. Defendant agreed to plead guilty to the crime as charged in the indictment and the Government agreed to recommend a three-point reduction of offense level for acceptance of responsibility. The parties also agreed that the provisions of 18 U.S.C. § 3553 governed the district court's consideration of Defendant's sentence. Subsection (a) lists numerous factors that a district court must consider in imposing a sentence that is "sufficient, but not greater than necessary" to comply with the enumerated sentencing purposes. Among those factors is "the need to avoid unwarranted sentence disparities among defendants with similar records who have been found guilty of similar conduct."1 18 U.S.C. § 3553(a)(6). After his plea hearing, Defendant filed a "Motion for Non-Guideline Statutory Sentence," in which he requested a sentence of time served. Defendant argued that U.S.S.G. § 5K3.1 created unwarranted sentence disparities within the meaning of subsection (a)(6) between defendants convicted of immigration offenses in non-fast-track districts, like himself, and defendants convicted of similar offenses in fast-track districts.

The district court denied Defendant's motion to vary from the recommended guideline sentence on alternative grounds. First, the court relied on our holding in United States v. Martinez-Trujillo, 468 F.3d 1266 (10th Cir.2006), to deny Defendant's motion. In Martinez-Trujillo, we held as a matter of law that sentence disparities created by fast-track programs were not "unwarranted" within the meaning of § 3553(a)(6). In the alternative, the district court denied Defendant's motion because he failed to present any evidence that he would be eligible for a fast-track program in a participating district. Based upon a finding that Defendant's recommended guideline range was "sufficient, but not greater than necessary," to achieve § 3553(a)'s sentencing objectives, the district court sentenced Defendant to 37 months imprisonment, the low end of the range.2 Defendant appealed. We exercise jurisdiction pursuant to 18 U.S.C. § 3742(a)(2), and uphold Defendant's sentence for reasons that follow.

II.

On appeal, Defendant claims his sentence is unreasonable because the district court erred in refusing to consider, as a matter of fact, whether sentence disparities between himself and defendants sentenced for immigration offenses under fast-track programs were "unwarranted" within the meaning of § 3553(a)(6). To support his claim, Defendant posits two arguments. First, Defendant argues that, given intervening Supreme Court precedent, our decision in Martinez-Trujillo is no longer viable and a district court now has the discretion to vary from the guidelines based on fast-track sentence disparities. Second, Defendant argues that because the Government shields the qualifications for fast-track disposition from defendants in non-fast-track districts, the Government should bear the burden of proving he is ineligible for a variance based on fast-track sentence disparities.

We ultimately review Defendant's sentence for reasonableness, deferring to the district court under the "familiar abuse-of-discretion standard of review." Gall v. United States, 552 U.S. 38, 46, 128 S.Ct. 586, 169 L.Ed.2d 445 (2007). Reasonableness "has a procedural and substantive component." United States v. Martinez, 610 F.3d 1216, 1223 (10th Cir.2010). Procedural error includes "failing to calculate (or improperly calculating) the Guidelines range, treating the Guidelines as mandatory, failing to consider the § 3553(a) factors, selecting a sentence based on clearly erroneous facts, or failing to adequately explain the chosen sentence—including an explanation for any deviation from the Guidelines range." Gall, 552 U.S. at 51, 128 S.Ct. 586 (emphasis added). On the other hand, "[a] challenge to the sufficiency of the § 3553(a) justifications relied on by the district court implicates the substantive reasonableness of the resulting sentence."3 United States v. Smart, 518 F.3d 800, 804 (10th Cir.2008). In this case, we review Defendant's sentence for procedural error because Defendant challenges the "method by which the sentence [was] calculated." United States v. Wittig, 528 F.3d 1280, 1284 (10th Cir. 2008). That is to say, Defendant challenges the district court's failure in the context of his case to even consider whether a sentence disparity caused by the existence of fast-track programs in some districts but not others is factually "unwarranted." We review the district court's legal conclusions in this regard de novo and its factual findings for clear error. United States v. Munoz-Nava, 524 F.3d 1137, 1146 (10th Cir.2008).

A.

The district court first denied Defendant's motion for a variance because we have "held repeatedly that the disparity created by the existence of `fast track' programs in other districts is not an unwarranted disparity within the meaning of [§] 3553(a)(6)." Record volume (Rec.vol.) II, at 54. The district court's assessment of Tenth Circuit case law undoubtedly is correct. In Martinez-Trujillo, we held as a matter of law that sentencing disparities caused by the existence of fast-track programs in some districts were not "unwarranted" under § 3553(a)(6), because such disparities were congressionally authorized. Martinez-Trujillo, 468 F.3d at 1268. We recognized that a district court must consider the entirety of the § 3553(a) factors, including factor (a)(6) regarding unwarranted sentence disparities, in imposing sentence, but opined that a disparity is not unwarranted where Congress specifically authorizes the disparity, such as the fast-track disparity in the PROTECT Act. Id.; accord United States v. Jarrillo-Luna, 478 F.3d 1226, 1231 (10th Cir.2007); United States v. Martinez-Macias, 472 F.3d 1216, 1219 (10th Cir.2007). Of course, Martinez-Trujillo and its progeny bind us "absent en banc reconsideration or a superseding contrary decision by the Supreme Court." United States v. Killion, 7 F.3d 927, 930 (10th Cir.1993).

Defendant submits that Kimbrough v. United States, 552 U.S. 85, 128 S.Ct. 558, 169 L.Ed.2d 481 (2007), is that "superseding contrary decision." In Kimbrough, a case addressing the disparity between guideline ranges for crack and powder cocaine offenses, the Supreme Court held that a district court had the discretion to vary from the recommended guideline range for a crack cocaine offense where the court determined such range was greater than necessary to achieve the sentencing objectives of § 3553(a). In other words, because the sentencing guidelines are advisory, district courts have the discretion to vary from those guidelines based on policy disagreements with them. In Spears v. United States, 555 U.S. 261, 265-66, 129 S.Ct. 840, 172 L.Ed.2d 596 (2009) (per curiam), the Court made plain Kimbrough's point; namely that regardless of individualized circumstances, "district courts are entitled to reject and vary categorically from the crack-cocaine Guidelines based on policy disagreements with those Guidelines."

At the time of Kimbrough, the applicable guideline provision treated one gram of crack cocaine as equivalent to 100 grams of powder cocaine. The Sentencing Commission developed this guideline by looking to the Anti-Drug Abuse Act of 1986 ("ADAA"), 100 Stat. 3207. The ADAA "treated every gram of crack cocaine as the equivalent of 100 grams of powder cocaine" by providing a five-year mandatory minimum sentence "to any defendant accountable for 5 grams of crack or 500 grams of powder" and providing a ten-year mandatory minimum sentence "to any defendant accountable for 50 grams of crack or 5,000 grams of powder." Kimbrough, 552 U.S. at 96, 128 S.Ct. 558. The government argued that while the guidelines are advisory, the 100-to-1 crack to powder ratio guidelines were an exception to a district court's sentencing discretion because the ratio was a congressional policy determination binding on the courts. Id. at 101-02, 128 S.Ct. 558. The Supreme Court rejected that argument because it lacked grounding in the text of the ADAA. The Court observed that the "statute, by its terms, mandates only maximum and minimum sentences." Id. at 102, 128 S.Ct. 558. Congress gave no directive "about the appropriate sentences within [the statutory minimums and maximums]" and the court declined "to read any implicit directive into that congressional silence." Id.

Absent a statutorily-mandated sentencing policy, Kimbrough authorized district judges to vary from the guidelines based on policy disagreements with those guidelines and not simply based on an individualized determination. As Spears makes clear, a district court pre-Kimbrough had the authority to issue a variance based on an individualized determination pursuant to § 3553(a)(6). However, in Martinez-Trujillo, we barred district courts from considering this disparity in the fast-track context.

Following Kimbrough's lead, we see nothing in the language of the PROTECT Act that reflects a congressional intent to restrict a district court's discretion in sentencing a defendant outside a fast-track district based on the sentencing of similarly-situated defendants inside a fast-track district.4 Undoubtedly, Congress provided "the Attorney General the ability to establish early disposition programs district by district, and instructed the Sentencing Commission to promulgate a guideline to implement those programs." United States v. Reyes-Hernandez, 624 F.3d 405, 418 (7th Cir.2010). But Congress "certainly did not explicitly forbid non-fast track districts from taking into account the effect of fast-track dispositions under the § 3553(a) factors." Id. Similar to the Supreme Court's reading of the ADAA, we simply cannot locate in the PROTECT Act "an implicit restriction on a district court's sentencing discretion."5 United States v. Rodriguez, 527 F.3d 221, 229 (1st Cir. 2008). Accordingly, our holding in Martinez-Trujillo must give way in light of Kimbrough.

Thus, we conclude that Kimbrough's holding extends to a policy disagreement with Guideline § 5K3.1 and further conclude that Martinez-Trujillo and its progeny must be overruled because a district court's consideration of a fast-track disparity "is not categorically barred as a sentence-evaluating datum within the overall ambit of § 3553(a)." Id. As the First Circuit explained, an intent to restrict the sentencing discretion of a district court in the context of fast-track disparity may be drawn from the statute "only by heavy reliance on inference and implication about congressional intent—a practice that runs contrary to the Court's newly glossed approach." Id. at 229-30. Just as the Supreme Court in Kimbrough declined to conclude that the crack to powder cocaine ratio was beyond the reach of § 3553(a), we conclude that fast-track disparity is not beyond the reach of § 3553(a).6 We hold that where the circumstances warrant, a district court in a non-fast-track district has the discretion to vary from a defendant's applicable guideline range based on fast-track sentence disparities; however, we emphasize that a district court still must calculate the applicable Guideline range without the four level benefit of § 5K3.1, consistent with the Supreme Court's holding in United States v. Booker, 543 U.S. 220, 125 S.Ct. 738, 160 L.Ed.2d 621 (2005). But our holding makes clear that district courts should not categorically exclude consideration of the absence of a fast-track program as they were required to do under our holding in Martinez-Trujillo.

In this case, Defendant challenged the disparity as an "unwarranted" disparity pursuant to § 3553(a)(6). We believe that, consistent with Kimbrough, a district court is not limited to consideration of that factor, but instead should consider the totality of the sentencing statute. Kimbrough, 552 U.S. at 108, 128 S.Ct. 558. In Kimbrough, the Supreme Court stated that the district court "must include the Guidelines range in the array of factors warranting consideration. The judge may determine, however, that, in the particular case, a within-Guidelines sentence is `greater than necessary' to serve the objectives of sentencing." Id. at 91, 128 S.Ct. 558. The court went on to hold that "[i]n making that determination, the judge may consider the disparity between the Guidelines treatment of crack and powder cocaine offenses." Id. "To reach an appropriate sentence . . . disparities must be weighed against the other § 3553(a) factors and any unwarranted disparity created by the crack/powder ratio itself." Id. at 108, 128 S.Ct. 558. In addition, "district courts must take account of sentencing practices in other courts." Id. Accordingly, a district court should engage in a "holistic inquiry" of the § 3553(a) factors in determining whether a defendant is entitled to a variance. Rodriguez, 527 F.3d at 228. Our holding today simply allows a district court to acknowledge a policy disagreement with Guideline § 5K3.1, and then consider the disparity between the Guidelines treatment of a defendant in a fast-track district versus a defendant in a non-fast track district in light of all of the 3553(a) factors to determine whether a within-Guidelines sentence is greater than necessary to serve the objectives of sentencing.7

B.

The district court ruled as an alternative to its application of Martinez-Trujillo that even if it had the discretion to consider fast-track disparity, no unwarranted disparity exists in Defendant's case. The district court based its conclusion on Defendant's failure to provide any evidence that he would qualify for a fast-track program in any other district. The court declined to reduce Defendant's sentence based upon dispositions given to defendants who do qualify for fast-track dispositions where Defendant had provided no evidence that he too would qualify. That brings us to our next question, namely, whether Defendant, as movant, has the initial burden of showing that he is eligible, at least in some sense, for sentencing consistent with a fast-track program.

At his sentencing hearing, Defendant asserted he did not bear the burden of proving eligibility for a program about which the Government does not publish the criteria for eligibility. Noting that Defendant had moved for a variance, the district court asked Defendant about the existence of any "anecdotal" evidence. Presumably, by the use of the term "anecdotal," the district court was referring to evidence of similarly situated defendants in fast track jurisdictions. Defendant responded that he could not answer whether he was eligible for a fast-track program. Defendant suggested the court ask the Government that question. Defendant simply asserted that because of the high volume of illegal re-entry cases in the district, he should be eligible for the fast-track program. With that, Defendant asserted the Government bore the burden of proving he was ineligible for fast-track sentencing.

The district court asked Defendant what type of people receive fast-track dispositions. Defendant again stated that he did not have access to that information and that the court should ask the Attorney General. The district court then followed up, asking whether Defendant had access to "anecdotal" evidence. Defendant's counsel responded that she "might be able to find anecdotal evidence," but she did not see why she should be required to provide that information to the court. Rec. vol. II at 46. The court observed that the motion for a variance was Defendant's. Counsel responded:

Id.

We acknowledge at the outset that Defendant's contention is not without some force. The Government, or more accurately the Department of Justice, refuses to release its criteria for determining eligibility for fast-track disposition. This inexplicable position leaves defendants charged with immigration offenses in non-fast-track districts in a quandary when forced to compare themselves to defendants charged with similar offenses in fast-track districts. The Government has provided no reasoned rationale for its steadfast opposition to shedding light on the factors it considers in determining program eligibility. But the Government's silence does not license a defendant to "sit on his thumbs," make no inquiry, and present no evidence that he is entitled to a variance based on fast-track disparity.

In this Circuit the law is well established that "the defendant shall bear the burden of proof for sentence decreases." United States v. Williams, 374 F.3d 941, 947 (10th Cir.2004) (quoting United States v. Kirk, 894 F.2d 1162, 1164 (10th Cir.1990)). The fast-track policy disagreement does not allow a district court to automatically grant a variance without the defendant somehow showing that he is entitled to the variance. In the cocaine context, a district court was instructed to determine whether a within-Guidelines sentence was greater than necessary to serve the objectives of sentencing, but the disparity was obvious because the 100:1 ratio was built into the Guidelines. In the present case, because not every illegal reentry defendant would necessarily qualify for fast-track disposition, after a district court articulates its policy disagreement with § 5K3.1, Defendant must bear some burden of proof to show he is entitled to a variance.

Consistent therewith, Defendant surely must make a minimum showing that a defendant charged with the same crime in a fast-track district would qualify for fast-track treatment. For example, Defendant might have contacted federal public defender offices in districts with fast-track programs to inquire about program eligibility requirements. Defendant also might have examined plea agreements of similarly situated defendants in fast-track districts. And those suggestions surely do not exhaust the possibilities of inquiry. Indeed, Defendant acknowledged he "might be able to find anecdotal evidence," but made no effort to look.8

As a consequence of Defendant's lack of industry, we need not determine today the exact showing a defendant must make in order to carry his initial burden of justifying a variance based on fast-track disparity beyond the minimum requirement discussed above. Suffice to say we agree with the Third Circuit that a "generalized argument" in which a defendant simply points to the disparity created by fast-track programs "is alone not sufficient to justify such a variance."9 United States v. Arrelucea-Zamudio, 581 F.3d 142, 156 (3d Cir.2009). That is the very argument Defendant makes here, and we reject it. The district court properly denied Defendant's motion for a variance because the court acknowledged that even if it could exercise its discretion, Defendant provided the court with no evidence to warrant a variance.

AFFIRMED.