The effects of adding alkyl sulfate surfactants to water-n-alkyl beta-D-glucopyranoside (C(m)beta G(1)) and water-alkyl ethylene glycol ether (CkOC2OCk)-C(m)beta G(1) mixtures are systematically explored. In a water-C(10)beta G(1)-sodium decyl sulfate (SDeS) mixture, miniscule amounts of SDeS (SDeS:C(10)beta G(1) molar ratio of 0.0025) cause the upper miscibility gap of the water-C(10)beta G(1) mixture to vanish. Adding small amounts of alkyl sulfates to water-CkOC2OCk-C(m)beta G(1) mixtures increases the surfactant efficiency, shifts the single-phase microemulsion region to higher temperatures, and shrinks the three-phase region. These phenomenological phase behavior observations are explained in terms of electrostatic effects introduced by the addition of an ionic surfactant to nonionic micelles and monolayers. Small-angle neutron scattering (SANS) measurements from several D2O-CkOC2OCk-C(m)beta G(1)-alkyl sulfate mixtures containing equal amounts of D2O and CkOC2-OCk are analyzed using a model for bicontinuous microemulsions. The values obtained from this analysis show that the monolayer spacing of D2O-CkOC2OCk-C(m)beta G(1)-alkyl sulfate mixtures grows with increasing ionic surfactant concentration, and this increased spacing accounts for the observed increase in surfactant mixture efficiency.