The oxygen nonstoichiometry of La2Ni0.95Al0.05O4.025 (+) (delta) (LNAO) is measured as a function of oxygen partial pressure (pO(2)) and temperature by coulometric titration method and thermogravimetric analysis (TGA) in 800 degrees C-1000 degrees C temperature range and 10(-16)-1 atm pO(2) range. The partial molar quantities for mixing of oxygen were calculated and results were compared with the literature results on La2NiO4 (+) delta (LNO). The variation in activity coefficient of holes versus oxygen nonstoichiometry illustrated an early positive deviation of the activity coefficient of holes from unity, leading to gamma h. approximate to 7 at delta approximate to 0.08, which was lower than the literature value of gamma(h). approximate to 14 for La2NiO4 (+) (delta) at delta approximate to 0.08, indicating lesser deviation of LNAO from ideal solution behavior. The effective mass of holes (m(h)*) was 1.02-1.21 times the rest mass (m(o)), which indicated the band-like conduction and allowed the effect of the small degree of polaron hopping to be ignored. The comparison of oxygen nonstoichiometry and partial molar quantities showed that incorporation of interstitial oxygen is less favorable in LNAO in comparison to LNO.