We report on the effects of Cr and Al on the microstructure and elemental partitioning behavior of gamma/gamma' forming Co-Ti-W-based alloys. Additions of Cr to a Co-15Ti-3W (at.%) base alloy at the expense of Ti led to a decrease in gamma' volume fraction, whereas Al additions at the expense of Co led to substantially increased gamma' volume fractions. Such alloy modifications resulted in reduced gamma/gamma' lattice misfits. Using atom probe tomography, we could show that Ti and W strongly partitioned to the gamma' phase, whereas Al and Cr partitioned to gamma. While Cr appeared to have only minor effects on the partitioning behavior of the other alloying elements, Al enhanced partitioning of Ti and in particular W to gamma', thus causing the observed increases in gamma' volume fraction.