Two loops; the north loop is open year-round. The south loop is open mid-May through September. There are also walk-in sites and a group site, off the south loop. The campground fills up almost every day in the summer, even during the week. Odd-numbered sites are reservable while even number sites are first-come, first-served. We were not able to get into the site we had reserved (a nice pull-through with views of the bluffs and the river) because the people staying there the night before were having difficulty with their RV and not able to move it. We had been re-assigned to Site 38, a much larger site, but among the trees with no view. We were bummed but had no choice as the campground was full. We thought we might try to move the next day, but it turns out friends were able to join us, so our large site ended up being to our advantage. The pull-through in Site 38 was so large that it could have easily accommodated three large Class A motorhomes with room to spare! Large picnic table that was pushed up against the trees; we discovered the next afternoon that it was to take advantage of as much shade as possible. No fire ring; campfires are permitted in charcoal bbq grates or fully contained fire pans. Wood was not available to purchase at the campground; you must go to Medora(about five miles away) to purchase or you can collect dead and down firewood. Bathroom was clean enough with flush toilets but NO SOAP! No showers but we didn’t expect them in a National Park campground. Several very short trails in the park but the most popular Petrified Forest Trail is accessible from outside the park. Saw bison, prairie dogs, pronghorn antelope, wild horses.