The app was developed over a six-month period, and the full version was first released in November last year.
Fuel prices on Gaspy are crowd-sourced, meaning users input the prices around the country and other users can track where the cheapest fuel outlets are.
Recent coverage of the app had led to a rapid rise in users, Green said.
"At the moment it's going up over 100 new users every day, and we're just about to crack 5000 app downloads."
It is free to download, and the gaming aspect - people can compete for points and prizes - meant it was fun for people of all ages.
"Courier drivers and truck drivers love it, and we see a big spike in holidays because kids do it from the back seat."
Green said they were on track to exceed 20,000 users within the next six months.