A method and apparatus for converting natural gas from a source, such as a wellhead, pipeline, or a storage facility, into hydrocarbon liquid stable at room temperature, comprising a skid or trailer mounted portable gas to liquids reactor. The reactor includes a preprocessor which desulfurizes and dehydrates the natural gas, a first stage reactor which transforms the preprocessed natural gas into synthesis gas, and a liquid production unit using a Fischer-Tropsch or similar polymerization process. The hydrocarbon liquid may be stored in a portable tank for later transportation or further processed on site.