A study was conducted to persue the effects of two biosurfactants (rhamnolipid produced by Pseudomonas aemginosa strain A41, and surfactin produced by Bacillus subtilis strain BBK1) and two synthetic surfactants (triton X-100, and oil-spill dispersant Chemtec 307) on Murban light crude- oil biodegradation by microorganisms isolated from petroleum-contaminated sand from Hua-Hin beach, Prachuabkhirikhan province and Pattaya beach, Chonburi province, Gulf of Thailand. It was found that bacterial isolate HU2 from Hua-Hin beach sand had the highest activity of crude-oil degradation. On the taxonomic indentification by 16S rDNA sequence analysis, isolate HU2 has 99.3% homology with the bacterium in the genus Brevundimonas and was therefore designated as Brevundimonas sp. strain HU2. Morphological and biochemical studies revealed a thin- bended and short rod-shaped organism, Gram negative, non-motility, 10% halotolerance, and non-biosurfactant - producer. This strain is able to utilize long straight chain n-alkane and various petroleum products, but failed to degrade polycyclic aromatic hydrocarbons (PAHs) and surfactants. Investigation of crude-oil biodegradation by the present strain was performed in BH broth supplemented with 1 % crude-oil and both sterile seawater and marine sand, pH 7.5 at 200 rpm agitation, 30°c, while bacterial growth was determined by viable plate count and residual oil were analysed by FTIR and GC-FID. After 8 days of biodegradation, the starting oil content was decreased down to 10.41 %, while that of abiotic degradation was found to be 77.83 %. Enhancement of biodegradation by the addition of 4 surfactants at a concentration equivalent to activity of oil displacement 78.6 cm2 and above their respective CMCs, rhamnolipid, surfactin, and Chemtec 307 enhanced the bacterial populations and completely oil degraded within 2 days, triton X -100 on the other hand achieved in 3 days. Augmentation of biosurfactant-producers (P.aemginosa strain A41 and B.subtiiis strain BBK1) also took 3 days to achieved the same result. As of abiotic control with surfactants addition after 4 days a 53.39-61.39 % of oil still. In addition, if surfactants were added at a concentration equal to or below the CMC (and at 0.01% concentration), an even slower rate of degradation was observed. It is also observed the present of nutrients in seawater and cultivation medium gave positive effects toward crude-oil biodegradation.