Please note that this is the Narutopedia's article on fire release technique. If you are looking for the article on the technique that utilises wind and fire then you should head to Toad Oil Flame Bullet.
This is a two-way cooperation ninjutsu. Gamabunta uses the Toad Oil Bullet technique to shoot a jet of oil from his mouth. His summoner then ignites the oil. Jiraiya uses the Fire Release: Flame Bullet technique for this purpose, while Naruto, knowing no Fire Release ninjutsu, opted to use explosive tags instead. The oil, acting as an accelerant, provides more fuel for the fire in an effect like a flame-thrower, and creating an conflagration of far greater power and magnitude than the original fire ninjutsu used on its own could have.