Nominally lattice-matched GaInAs layers grown by metal organic vapor phase epitaxy on InP substrates have been studied using high-resolution x-ray diffraction (HRXRD) to determine the growth conditions under which ordering is introduced.  HRXRD provides an independent means to quantify the order parameter of semiconductor heterostructures as well as the ordering on different {111} planes, i.e., double variant ordering.  This independent means to determine ordering provides for a better understanding of the effects of ordering on the electronic and optical properties. Double variant ordering was observed for epitaxial layers grown on exact (001) InP substrates, with an order parameter of about 0.1 in both variants.  For substrates that were miscut by 6 degrees, single variant ordering was detected.  In these cases, an order parameter as high as 0.66 was measured for certain growth conditions.  The layers grown on vicinal substrates are all of high crystalline quality, those on (001) substrates exhibit some mosaic spread.