The main gas-to-liquids (GTL) interest now is in Fischer-Tropsch (F-T) synthesis of hydrocarbons. While synthesis gas (syngas) for GTL can be produced from any carbon-based feedstock (hydrocarbons, coal, petroleum coke, biomass), the lowest cost routes to syngas so far are based on natural gas. Thus, the focus for GTL has been largely on associated gas, so-called stranded or remotely located gas reserves, and larger gas reserves that are not currently being economically exploited. The principal technologies for producing syngas from natural gas are: catalytic steam methane reforming (SMR), two-step reforming, autothermal reforming (ATR), partial oxidation (POX), and heat exchange reforming. The distinguishing characteristics of these technologies and their commercial uses are discussed in this paper. Ongoing R&D efforts to develop lower-cost syngas generation technologies are also briefly discussed. Relevant commercial experience with large-scale syngas generation for GTL is also discussed. As a frame of reference, in terms of syngas flow rates, a 20,000 b/day F-T plant would be comparable to three 2500 mt/day methanol plants. Single-train methanol plants are now producing more than 2500 t/day-and plants approaching 3000 mt/day have been announced. The projected relative economies of scale of the various syngas production technologies indicate that two-step reforming and ultimately, ATR, should be the technologies of choice for large-scale GTL plants. Nevertheless, for a 20,000 b/day F-T liquids plant, capital charges still dominate the manufacturing costs. Syngas production (oxygen plant and reforming) comprises half of the total capital cost of this size GTL plant. While air-blown reforming eliminates the expensive oxygen plant, air-blown reforming is unlikely to be competitive with, or offer the flexibility of, oxygen-blown reforming. The reasons for this conclusion are discussed. The proposed and future GTL facilities should be substantially less costly than their very expensive predecessors-as the result of improvements in FT catalyst and reactor design, the most significant of which have been pioneered by Sasol. In the absence of a breakthrough technology, economy of scale will be the only significant mechanism by which GTL can achieve greater economic viability. However, even with such further cost reductions, the economic viability of GTL plants will remain confined to special situations until crude price levels rise substantially. In the long term, if a ceramic membrane reactor (combining air separation and partial oxidation) can be developed that enables the 20% reduction in GTL investment costs that the R&D effort is targeting, GTL could become economically viable at crude prices below US$20/b.