Biodegradation of petroleum model compounds by microbial mats from Saudi Arabia at various salinities. The data are expressed as percentages relative to the initially added amounts (i.e. 3.33 mg of each model compound adsorbed on 100 mg of organo-clay complex particles). Dotted bars, pristane; cross-hatched bars, n-octadecane; black bars, phenanthrene; white bars, dibenzothiophene.