Legume inoculants are products that introduce legume-specific rhizobia bacteria to the soil and promote the process of biological nitrogen fixation. Guar (Cyamopsis tetragonoloba L. Taub.), also known as clusterbean, is a legume produced in semi-arid regions around the world, primarily for industrial uses of guar gum, but there is only one known commercial inoculant products for the crop, which is not available worldwide. The USDA-ARS National Rhizobium Germplasm Collection has four Rhizobium strains listed as compatible with guar: USDA 3089, USDA 3385, USDA 3386, and USDA 3595. The objective of this research was to test the efficacy of four peat-based, seed-applied inoculants derived from these strains, as well as a mixture of all four strains, compared with un-inoculated plants in controlled greenhouse conditions. Among the tested strains, USDA 3089 and USDA 3386 had the greatest positive impacts, as they increased nodule weight, total assimilated nitrogen, biomass production, and protein production per plant relative to the un-inoculated control. USDA 3385 and the Mix likewise increased nodule weight. No inoculant affected other measured aboveground plant morphological and productivity parameters or nodule number. These Rhizobium strains, particularly USDA 3089 and 3386, were identified as beneficial and recommended for further testing in the field in development of an effective inoculant for guar.