A Calgary app developer is reaping the rewards after its latest mobile game has become an international success.

"This is huge for us. This is extremely exciting," said Doug Junor, one of the heads of Calgary-based Robots and Pencils.

"I think we knew that we had a good game. I don't think we knew how big it was potentially going to get."

As of Saturday, the game company’s Spy vs. Spy game was still the top seller in Apple’s App Store, a spot it has held for a week.

Paul Thorsteinson, lead designer for the company, had the idea to develop the game as an app after being inspired by the original Commodore 64 version of the game, which he used to play as a child with his father.

"I knew it would do well. I felt in my heart that it would."

It took two years and around $500,000 to develop the game, Thorsteinson said.

The game made it into the top 20 apps on its first day and kept climbing.

"I had been watching it every three minutes," he said.

"It's like getting a blockbuster in the movie industry."

Despite the strong sales, Robots and Pencils says it is just now getting close to breaking even on the game.