Selective, irreversible removal of hydrogen sulfide (H.sub.2S) and other sulfhydryl compounds from a gas stream, such as sour natural gas and sour hydrocarbon liquids is achieved with a scavenging agent having hydroxyalkyl functionality and alkylamine functionality. This scavenger possesses a higher capacity for H.sub.2S removal compared with a scavenger having only hydroxyalkyl functionality. The scavenging agent is made by reacting at least one alkanolamine and at least one alkyl amine with an aldehyde, such as formaldehyde.