Most orioles are attracted to nectar and/or fruit. The bright orange color of the nectar feeders also attracts orioles and means you don't need to use artificially colored nectar. Ideal foods inlcude nectar (sugar solutions you can buy or make), orange halves or sections, and jelly (especially grape jelly).
And you can purchase ant moats ▶
separately for feeders that don't have them built in."Hey, hon, how 'bout dem O's!!!"