Russia had a oil concession in Vietnam but pulled out after China harassed the operations.
Malaysia oil operations extend up to disputed border with Vietnam and Thailand where instead of quarrelling, all decided to do a joint exploration. All these done in the 1990's when China was still weak. Now it's too late. Oil platforms are all over Malaysia part of South China Sea. Except in disputed border with Philippines as Philippines still has a claim on Sabah which they refuse to let go. If they had resolved the matter petronas oil rigs and platforms would have dotted the West Philippines sea as well.