CALGARY, Alberta - For the past six years, the bull riding at the Calgary Stampede has been won by a PBR rider. This week, top Built Ford Tough Series competitors are attempting to continue that streak at the rodeo's centennial celebration.

They call it, "The Greatest Outdoor Show on Earth."

"There are a few rodeos that are known worldwide," PBR Livestock Director Cody Lambert said last week at the start of the 10-day event. "If they've heard of rodeo, they've heard of the Calgary Stampede. It's been that way forever. There's not any generation of rodeo that the best guys didn't compete there."

The Stampede's history includes an all-star list of bull riding greats and PBR founders. Jim Sharp won the bull riding at the Stampede in 1987. Lambert won the all-around in 1990 and Ty Murray won it in 1998. Both rode broncs and bulls to secure their all-around wins. Adriano Moraes won the bull riding title in 1994.  J.W. Hart rode to victory in 1997.

The rodeo always drew the cream of the crop, but in 2006, the Stampede went to an invitational format, selecting only the top competitors in each event.

A PBR rider has won the bull riding trophy every year since then. Ross Coleman started the streak in 2006. In subsequent years, the trophy was won by Brian Canter, Mike Lee, J.B. Mauney, and Douglas Duncan. Shane Proctor took it home last year.

The payout is huge. This Sunday, the event winners will each be presented with a $100,000 check. Stampede promoters call it "rodeo's richest afternoon."

"The Calgary Stampede was one of the very first big money rodeos ever," Lambert said. "It was definitely the first place that you could win $50,000 in one place, and the first place a contestant could win $100,000 in one place. It's a level playing field for the best contestants for the most money. And that's exactly what the PBR is all about. The Calgary Stampede is a pioneer in that way."

"The PBR riders, day in and day out, face tougher bulls than anyone, and ride for more money on bigger stages than anyone." 

This year, Mauney, Proctor, Austin Meier, L.J. Jenkins, Kody Lostroh, Aaron Roy, Robson Palermo, Luke Snyder, Ty Pozzobon and Caleb Sanderson are among the BFTS regulars competing in Calgary. 

Lambert thinks one of them will win. 

"The PBR riders, day in and day out, face tougher bulls than anyone, and ride for more money on bigger stages than anyone," he said. "Those guys are capable of winning everywhere they go."

It's not just the money that makesCalgarysuch a prized invitation. The history, the atmosphere and the fans combine to create an unparalleled experience.

"It's an amazing event," Proctor said. "The whole committee, the whole town - pretty much the whole province of Alberta come together to celebrate these 10 days. It's a really fun atmosphere to ride in."

Duncan, who won in 2010, agreed. 

"There's so much history behind it," he said. "It's just as big as getting to your first PBR Finals.

"They're diehard fans. I've seen it pouring down rain and half the stands are uncovered and not one person got up. They're there to watch it, and they're not scared to get drenched."

The unique tournament-style format adds to the excitement. Divided into two pools of 10, riders start out by facing one bull a day for four days. Each pool then sends its top four riders to "Showdown Sunday" on the last day of the Stampede. 

Pool A included Mauney, Proctor, Roy, Meier, Chad Besplug, Tyler Thomson, Wesley Silcox, Tyler Willis and Tyler Pankewitz. Roy, Meier, Besplug and Silcox have already secured a place in Sunday's finale.

Today, Jenkins, Lostroh, Palermo, Snyder, Sanderson, and Pozzobon, along with Dusty Ephrom, Denton Edge, Scott Schiffner and Jacob O'Mara are competing in Pool B for the next four slots.

A wild card round on Saturday will give the remaining six riders from each pool a chance at the final two spots in Sunday's winner-take-all showdown.

"It really means a lot to the riders to win," said Lambert, whose trophy has a place of honor in his living room. "I'd hate to think I'd ridden my whole career and never ridden in the Calgary Stampede. That's one of the highlights of my rodeo career."