According to Cattell's [Cattell, R.B. (1987). "Intelligence: Its structure, growth and action." New York: North-Holland.] Investment theory individual differences in acquisition of knowledge and skills are partly the result of investment of Fluid Intelligence ("Gf") in learning situations demanding insights in complex relations. If this theory holds true "Gf" will be a factor of General Intelligence ("g") because it is involved in all domains of learning. The purpose of the current study was to test the Investment theory, through investigating the effects on the relation between "Gf" and "g" of differential learning opportunities for different subsets of a population. A second-order model was fitted with confirmatory factor analysis to a battery of 17 tests hypothesized to measure four broad cognitive abilities The model was estimated for three groups with different learning opportunities (N = 2358 Swedes, N = 620 European immigrants, N = 591 non-European immigrants), as well as for the total group. For this group the "g-Gf" relationship was 0.83, while it was close to unity within each of the three subgroups. These results support the Investment theory. (Contains 1 figure and 10 tables.)