Introversion Games has earned more than US$19 million in revenue from sales of management sim Prison Architect.

In an interview with Eurogamer, Introversion games co-founder Mark Morris revealed that the game has sold more than 1.25 million copies since it launched on Steam Early Access program in September of 2012.

Introversion co-founder Chris Delay also revealed that the studio, formed in 2001, was on the edge of closing before the game's success.

"We don't take anything for granted anymore," said co-founder Chris Delay.

"After Defcon's launch we were in really rude health, really solid health, and within four years we were almost gone.

“You can blow your money very quickly in video games."

However, Morris said that they are on stable footing once again due to the success of Prison Architect.

"The company is very, very healthy," Morris said

"Also, we think that Prison Architect could be the biggest hit of the next 15 years at Introversion, so we've been very prudent with what's happening with the resources that it's generating, because we know that we can never run out of money again now.

“Not because we've made so much, but because it would be criminally negligent if we ever had to go back cap in hand."

Morris and Delay said that they intend to continue support of Prison Architect "almost certainly the whole of next year”. However, the pair is already working on a new concept, which they say will ramp up production after the launch of Prison Architect.

After three years in Early Access, Prison Architect will be officially released on October 6.