Alternative formats for load combination requirements in structural design codes are examined. Basic alternative models of macro load-time dependence for live, snow, wind, and earthquake loads are reviewed and a sensitivity analysis performed to establish a set of models sufficient for combination studies. On the basis of normalized design loads and a spectrum of influence coefficients, load combination factors in the alternative basic code formats are established. Extensive numerical results are presented for possible use in code development, It is concluded that a companion action approach is preferable to a probability reduction factor approach and a set of potential design values is suggested.