Brunei. (British Bechuanaland). 1951. Envelope written from 'Sarawak Oilfield Ltd./ SERIA/ State of Brunei via Singapore' (with boxed cachet in red on reverse) addressed to New York bearing Brunei SG 86, 15c ultramarine tied by Kuala Belait date stamp with framed arrival 'Received Mar 5' and forwarded to Rakop, British Bechuanaland bearing Bechuanaland postage dues SG D4, 1/2d sage green, SG D5, 1d carmine and SG D6, 2d violet tied by Tsienyane double ring '20th 1V 51' on face.
The town of Seria did not exist until oil was found in 1929. The Post Office opened (10.6.51).
Very rare combination.