In this dissertation, I examine the role of population and transportation costs in determining agricultural expansion in 670 villages located in Forest Reserves of Thailand, over the period 1986-1996. Specifically, I examine the role of population and transportation costs as drivers of agricultural decisions regarding crop adoption and area planted, and in determining the intensity of cultivation and agricultural expansion. I also contrast the impact of these variables on two groups of villages in Forest Reserves - villages whose residents 'have no secure property rights' and those whose 'land rights are ambiguous'. I examine Feder et al.'s (1988) conclusions about the importance of property rights in Thai forest reserves and find that there is some evidence supporting their conclusions in this study. Differences in property rights account for some difference in the agricultural decisions of the two groups of villages, but that the nature of data does not allow a sharper distinction. Results reported in the study are consistent with other studies of the area. The study suggests that decisions regarding crop adoption and crop area are sensitive to population but the magnitudes of impact are small. Lack of significance of transport costs in determining cropping decisions suggests that rural road building programs will not necessarily promote deforestation in the study area, contrary to evidence in other parts of the world. This is particularly important given the large number of Forest Reserve residents in Thailand, and the fact that, Forest Reserves are the last bastions of forests, and consequently of biodiversity, in Thailand. One policy implication of this is that investments in roads that help to increase access to markets and aid poverty alleviation may not have the deleterious effects on forests that would otherwise be expected.