Britain's Far East problem was moving oil, not finding it

Had Britain stockpiled significant oil at Singapore?

Yes; Britain held large Far East stocks, so the harder problem was distributing the oil rather than acquiring more of it.

Britain had accumulated large oil reserves at Singapore and elsewhere in the Far East, including Australia. The regional problem was therefore not simply whether fuel existed. Ships, bases, and forces still depended on moving those stocks to the places where operations required them. This distinction between supply and distribution reinforces the earlier Pearl Harbor discussion: storage capacity has limited value when pumping, transport, or access to the fleet is disrupted.