A static mixer includes a tubular body having a sidewall with an upstream end, a downstream end opposite the upstream end, and an inner surface. The upstream end has a surface defining an upstream opening into the body. The downstream end has a surface defining a downstream opening exiting the body. The upstream opening, the downstream opening, and inner surface define a passageway through the body for transport of a first fluid therethrough. A primary fin may depend from the inner surface of the body and into the passageway. The primary fin may have a curved fin with a flow surface. A secondary fin may extend into the passageway adjacent to the primary fin, the secondary fin may have a curved flow surface that curves opposite to the flow surface of the primary fin. The secondary fin may be offset upstream or downstream from the primary fin.