The leak at the Shell petrol station along Sembawang Road on Monday was an isolated case and no one was hurt during the incident, said the oil company.
The Shell spokesman was speaking to The Straits Times during a visit by Foreign Minister K Shanmugam to the station on Thursday morning.
The Singapore Civil Defence Force was notified about the matter at about 5.50pm on Monday.
Upon arrival, the officers used foam to contain the leak.
Mr Shanmugam, who is also Law Minister and MP for the area, said he has been kept informed on the developments over the last few days.
"Shell has assured me that the leak has been contained... to the premises of the station and they have been monitoring the vapour levels and they are at normal, not elevated."
The minister added that there needed to be "faster communication" as to what was happening as residents were concerned.