Mahayana Buddhism is the most popular and alongside Ancestor Worship, Taoism and Confucianism as one which is the traditional faith of general Han Chinese people (about 15% of total population of Brunei).
From many estimates of different sources but the most common figure today is 14% of Brunei's population are Buddhists.
And Buddhism is also the second largest religion after state religion of Brunei: Islam.
- CIA FactBook - Brunei 
- The US State Department's International Religious Freedom Report 2006 - Brunei 
- Religious Freedom page - Brunei 
- Religious Intelligence - Brunei