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The use of air–water, θ_wa, or air–liquid contact angles is customary in surface science, while oil–water contact angles, θ_ow, are of paramount importance in subsurface multiphase flow phenomena including petroleum recovery, nonaqueous phase liquid fate and transport, and geological carbon sequestration. In this paper we determine both the air–water and oil–water contact angles of silica surfaces modified with a diverse selection of silanes, using hexadecane as the oil. The silanes included alkylsilanes, alkylarylsilanes, and silanes with alkyl or aryl groups that are functionalized with heteroatoms such as N, O, and S. These silanes yielded surfaces with wettabilities from water wet to oil wet, including specific silanized surfaces functionalized with heteroatoms that yield intermediate wet surfaces. The oil–water contact angles for clean and silanized surfaces, excluding one partially fluorinated surface, correlate …