The hydroformylation of 1-dodecene under aqueous/organic two-phase reaction conditions with rhodium catalysts derived from BISBIS (sodium salt of sulfonated 2,2'-bis (diphenylphosphinomethyl)- 1,1'-biphenyl) in the presence of cationic surfactants was studied; regioselectivities appear to be sensitive to pressure. In all cases, the activities and regioselectivities for linear aldehyde were higher.