Biomarkers in fluid inclusions can constrain source regimes for hydrocarbons associated with Mississippi Valley-type Pb-Zn deposits. Significant amounts of hydrocarbons have been detected in fluid inclusions in sphalerite and dolomite intimately associated with Pb-Zn sulfides in the Canning Basin, Western Australia. The hydrocarbons are more mature than those in the host rocks to the ore and are therefore derived from an external source. Furthermore, there are differences between the biomarker components of hydrocarbons in inclusions in Pb-Zn prospects, but they are all different from hydrocarbons in organic-rich strata and also in oils from the Canning Basin. Yet, the hydrocarbons are mature and oil-like, suggesting that mature organic-rich strata deeper in the basin, which are less significant as potential source rocks for petroleum generation in the Canning Basin, have contributed to the ore-forming fluids.