Soybean [Glycine max (L.) Merr.] oil with increased oleate content may be useful for certain food and industrial applications requiring increased oxidative stability. M23, obtained Saga University, Japan, is a mid-oleate line developed by X-ray irradiation with twice the oleate content of normal soybean cultivars. The first objective of this study was to determine if molecular selection for the ol allele associated with the deletion of Fad2-1 could identify mid-oleate individuals in the F 2 population of 'Archer' x M23. The segregation among F 2 plants satisfactorily fit a ratio of 1 homozygous OlOl: 2 heterozygous Olol: 1 homozygous olol. The second objective was to determine how modifying genes affected the oleate content of olol individuals from the 'Archer' x M23 population. The distribution for oleate of the olol class overlapped that of the OlOl and Olol classes, which indicated that modifying genes significantly influence the oleate content of olol individuals. The third objective of this study was to determine if three mid-oleate lines: FA22 from Iowa State University, N98-4445A from the USDA-ARS/North Carolina State University, and M23 contain different genes that control their mid-oleate content. The single-cross populations FA22 x M23, FA22 x N98-4445A, and N98-4445A x M23 were developed. Plants with greater oleate than the parents were observed in the F2 and F 3 generations of the three populations. The F3:4 line with the greatest oleate content had 689 g kg-1 in the population FA22 x M23, 672 g kg-1 in FA22 x N98-4445A, and 730 g kg -1 in N98-4445A x M23 compared with 542 g kg-1 for FA22, 589 g kg-1 for N98-4445A, and 583 g kg-1 for M23. Transgressive segregates from the populations should be useful as parents in a breeding program to develop cultivars with elevated oleate content. A fourth objective of this study was to determine if the mid-oleate from M23 could be incorporated into soybean lines of MG I to IV that had low saturates, reduced linolenate, or low saturates + reduced linolenate. Soybean lines of MG IV and earlier were developed with the desired combination of fatty esters.