They also need to determine what caused the leak, but at this stage, there's no information released about what might have happened.
NASA said: "Flight controllers will monitor pressure trends overnight".
According to NASA the crew was never in danger and will return to their regular schedule on Friday.
Halle Berry jokes about teenage Prince Harry's dorm room poster of her
There are also two cut-out bikini shots of women either side of Berry's picture but the photograph does not reveal their faces. Berry, possibly flattered upon seeing the room of the prince, made a decision to poke fun at him.
The astronauts were asleep at the time, but when they rose for their day's work on Wednesday they were instructed to search for the leak.
Even with the scary thought the space crew could have run out of oxygen, NASA and Russian space officials have stressed all six astronauts on the ISS were and are in no danger.
Six people are now orbiting Earth aboard the ISS - Nasa astronauts Drew Feustel, Ricky Arnold and Serena Auñón-Chancellor, as well as Gerst, who is German, and two Russian cosmonauts - Oleg Artemyev and Sergei Prokopyev.
The 400km high outpost is home to three Americans, two Russians and one German.
A NASA spokesperson stated that they could not speculate at the moment if the three astronauts must return earlier or not, in case the small leak cannot be stopped.