AbstractApplying the manometric method, the solubility of hydrogen in alloys Ti1‐xGaxwas studied in the range 0 ≦x≦ 25; 5 · 10−5≦pH2/bar ≦ 1; 773 ≦T/K ≦ 1298. Within the given range ofpandTthe phase diagram of Ti1‐xGaxHrwas investigated for 9 compositionsx. In the range of solid solutions, 0 ≦x≦ 0.11, with increasingxthe range Δrof the hcp phase α‐Ti1‐xGaxHrincreases slightly, whereas the range of the bcc phase β‐Ti1‐xGaxHr, narrows strongly with increasingx. The width Δrof the two phase region α + β is nearly independent ofxand the phase boundary between β‐phase and (β + γ) region shifts with decreasing Δrof the β‐phase to smallerr. In α‐T1‐xGaxHrthe enthalpy of hydrogen solution ΔHHis practically independent ofrbut depends slightly onx, decreasing from ‐46.0 kJ mol−1(x= 0) to ‐46.5 kJ mol−1(x= 0.10). In the bcc phase β‐Ti1‐xGaxHr, ΔHHdecreases markedly from ‐57 kJ mol−1(r→ 0) to ‐70 kJ mol−1(r⇌ 1). ΔHHis independent of the gallium contentxwithin the limits of error. — Assuming a plausible blocking model for the occupancy of interstitial sites in the metal matrix by hydrogen, the excess entropies of dissolved hydrogen were evaluated. In α‐Ti1‐xGaxHran increase of ΔSEHis found with increasingrfrom ‐55 JK−1mol−1(r→0) to ‐53 JK−1mol−1(r= 0.1). ΔSEHdepends much stronger onrin β‐Ti1‐xGaxHr: ΔSEH= ‐70 JK−1mol−1(r→0); ΔSEH= ‐66.5 JK−1mol−1(r= 0.8). There is negligible influence ofxon ΔSEHin both phases. — In the ordered hcp phase α2‐Ti3GaHrthere is an increase of exothermicity compared to α‐Ti1‐xGaxHr. ΔHH(r→ 0) is ‐51.3 kJ mol−1for the ordered phase and it depends onr, increasing to ‐50 kJ mol−1atr⇌ 0.1. ΔSEHfor this phase is independent ofr, ΔSEH