Low gas prices and the affordability of a trip to Yellowstone National Park fueled a record-setting month in American's oldest national park -- by a huge margin. Over 900,000 people entered Yellowstone in July; up 11.4 percent from the same month in 2008, and up over the previous all time record of 847,000 visitors set in July 1995.

All park entrances reported an increase in the number of visitors compared to year ago levels. The West Entrance remains the park’s busiest, with over 385,000 visitors this July compared to 337,000 a year ago. The greatest percentage increase in visitation was recorded through the East Entrance, up 15.1 percent from July 2008.

July is typically the park’s peak visitation month, followed by August, June, September, and May.

This is the second record setting month for the park this year. Visitation in June was just under 644,000, well above the previous record of 609,000 visitors in June 2007.

For the first seven months of the year, over 1.9 million people have visited Yellowstone. That’s up 100,000 from the previous record of 1.8 million recorded in 2007. The park may be on a pace to break the annual visitation record of 3.15 million set in 2007.

Park managers believe the decrease in gasoline prices from over $4 a gallon last July to near $2.50 a gallon this summer helped spur the increase in visitation.

The National Park Service is offering three fee-free weekends to encourage Americans to visit their national parks this summer. The free admission weekend of July 18-19 is also believed to have contributed to the high visitation levels. The next fee free weekend is set for August 15-16.

Keep up with the latest in Yellowstone National Park news with our free weekly Yellowstone Insider newsletter. Subscribe today! More details here.

Follow Yellowstone Insider on Facebook! Click this link to go to our Facebook page, which features story updates.

We've also set up a free Twitter account so you can receive updates on the device of your choice.