Based on our present knowledge, the only long-term practical solution to sustaining a national economy on natural gas is to convert a major source of continuously renewable nonfossil carbon to substitute natural gas that is interchangeable with, or can be substituted for, natural gas. The most promising source of this carbon is land- and water-based biomass produced from solar energy by photosynthesis. An assessment of this concept is presented in this paper, and the major problems encountered in the development of the technology are reviewed. The technology for biomass production and conversion is sufficiently advanced so that break-throughs and discoveries of a fundamental nature are not required. Special emphasis is given to the importance of system design, biomass production, biomass conversion to SNG, economics, and energetics. A concept for the Net Energy Production Ratio of fully integrated systems is also presented. After suitable development, the commercialization of an SNG industry using low-cash-value, high-fuel-value biomass raw materials will probably be economically attractive. It is essential to start a full-scale development program now so that the technology is ready for use before fossil fuel depletion causes even greater energy supply problems.