Abstract This paper examines two policy rules for intergenerational equity in a model of optimal capital accumulation and resource extraction. First, we introduce Hartwick's rule (1977. American Economic Review 66, 972–974) for a constant consumption path and also consider relationships between Hartwick's rule and conservation laws. Second, by using conservation laws, we investigate another rule for a constant utility. This paper also attempts to derive the investment rule for Benthamite utility maximization.