Lake Placid 3

A year after the events of the second film at Black Lake, in Aroostook County, Maine, young couple April and Jason go skinny dipping and are attacked and eaten by a group of baby crocodiles. Meanwhile, at the house of the deceased Sadie Bickerman, her nephew Nathan, his wife Susan, and their son Connor, are cleaning out the house so they can sell it. However, Sheriff Tony Willinger soon arrives and convinces Nathan and Susan not to sell. Connor chases an escaped pet lizard down to the lake where he encounters the baby crocodiles, and begins to secretly feed them.
Two years later, Connor has continued to feed the now adult crocodiles stolen meat from the supermarket, but he is soon caught for shoplifting by Dimitri and sent home to his babysitter, Vica, by Susan. However, Connor goes to the lake to feed the crocodiles, followed by Vica who is attacked. Vica, whose arm has been badly injured, finds Susan at Sadie's house, where they tend to Vica's arm and Connor confesses to feeding the crocodiles. Meanwhile, Nathan is searching the lake due to a number of elk disappearances. He meets four teenagers; Ellie, Tara, Aaron, and Charlie who are camping on the lake. The teenagers show Nathan an elk head they previously found, leading Nathan to believe it was the act of hunter Reba, but he persuades Sheriff Tony to search the lake to make sure it is clear of crocodiles. While the teenagers camp, they decide to go swimming and the girls go into the woods and strip of their clothes naked and into their bikinis. Charlie spies on them and watches them stripping their clothes and by taking pictures, but then is devoured by a crocodile.
Reba is approached by teenager Brett, to help him find his girlfriend Ellie, who he fears will be taken advantage of by Aaron. Reba agrees and takes Brett out onto the lake in her boat with Jonas and Walt. Stopping to hunt elk, a crocodile attacks the boat and knocks the group into the water. Walt is devoured, but the others escape to shore and are stranded in the woods. After hours, Ellie and Aaron search for the missing Charlie, leaving Tara by the lake where she reveals her breasts, thinking it is Charlie and then is attacked by a crocodile that drags her into the lake. Ellie and Aaron return to find Tara missing, so they decide to try and get help. They discover Charlie's corpse, before finding what Ellie thinks is Brett's jacket. Ellie decides to search for Brett, upsetting Aaron who walks the other way, only to be attacked by a crocodile.
After searching the lake, Nathan and Sheriff Tony arrive at Sadie's house and reunite with Susan, Connor and Vica. They decide they should try and escape the house to go to a hospital, but in their attempt, Vica and Sheriff Tony are devoured and the car is submerged in the lake. Nathan, Susan, and Connor take shelter in the house. Meanwhile, Brett, Reba, and Jonas manage to shoot a crocodile dead, but another crocodile arrives and decapitates Jonas before attacking Reba, who manages to escape. Desperate, Reba and Brett travel on Reba's boat to Sadie's house and meet with Nathan, Susan and Connor. Determined to find Ellie, Brett escapes to Reba's boat and searches for her. He finds Ellie, but a crocodile kills him.
Reba kills a crocodile that breaks into the house, before she leaves with Nathan, Susan and Connor. Ellie joins them, and they make it to the town. The group break into the supermarket to call for help, setting off the alarm that attracts Dimitri, but he is swiftly devoured as a group of crocodiles enter the supermarket. The group is ambushed but manage to kill most of the crocodiles, but Reba is seemingly killed in the process. The only remaining crocodile chases Nathan, Susan, Ellie, and Connor to the gas station where the group manage to ignite gas with a lighter, causing an explosion that kills the crocodile. An ambulance then comes and helps Nathan, Susan, Ellie, and Connor.
Sometime later, Nathan, is taking a group of tourists around the lake, telling them of the crocodiles that are believed to be extinct. However, a baby crocodile is seen swimming in the lake, before an adult crocodile attacks the camera and the film ends.

Question: What do the characters ignite to kill the last crocodile?
Answer: gas