STURGIS, S.D. -- The 68th annual Sturgis Bike Rally is under way in South Dakota's Black Hills.

Each year, hundreds of thousands of bikers descend on Sturgis, expanding the town's regular population of just over 6,000 residents to a half-million.

Early reports suggest numbers are down for this year's rally, both in registered vendors and rally riders. Hoteliers told the Rapid City Journal that fewer rooms were booked in advance, and that fewer trailers were parked in their lots. In the past, many bikers have trailered motorcycles to Sturgis. But business owners speculate that high gas prices put more rally riders in the saddle since motorcycles generally get better gas mileage than cars. The paper reported that vendor numbers were down about 15 percent compared with 2007.

The official rally dates are Aug. 4-8, but bikers hang out in western South Dakota before and after The Rally, making it about a three-week event.

The Rally started in the '30s as a series of races for Harley-Davidson and Indian motorcycles, according to SturgisRallyDaily.com. It has morphed into an event that combines competition, fashion, road rides, shopping, eating, concerts and more for bikers of every stripe and motorcycles of every make and model. See more of this year's event by clicking through the slideshow.