Natural gas provides a current, low-cost alternative to the use of gasoline and diesel fuel for highway transportation vehicles. However, due to the capital costs required to use natural gas as a transportation fuel in either compressed (CNG) or liquefied (LNG) forms, some applications are more advantageous than others. Generally, fleets provide the best opportunity for conversion because of the sheer volume of fuel required and because most vehicles return to a single location each day. The advent of small compressors may make conversion to natural gas feasible for private individuals.Presently, the most popular conversions are to CNG due to the limited availability of liquefiers to produce LNG. The available conversion kits favor vehicles with certain characteristics: vehicles should have spark-ignition engines, be large enough to support the weight of the CNG fuel cylinders, consume at least 5 gallons of gasoline each day on average and have sufficient storage volume so that the fuel cylinders do not infringe on required load-carrying volume. The ease of conversion depends greatly on the vehicle. Pickup trucks are usually easy to convert while subcompact cars can present formidable challenges due to space requirements and load-carrying capacity.The costs of converting to CNG include vehicle conversion costs, refueling station costs, and required operating and maintenance costs. These costs vary according to vehicles (how many storage tanks and how difficult the conversions are), the planned utilization of compressor capacity, whether the vehicles are refueled using slow-fill or fast-fill techniques and the refueling site preparation required. In this paper, these costs are explained and compiled for the conversion kits and refueling equipment presently available. A few case studies are explored to demonstrate what must be known to evaluate whether a fleet of vehicles has potential to save money using natural gas and how long it may take to see a return on the initial investment.Also discussed in the paper is an overview of CNG safety aspects, especially as related to road and operating restrictions that may exist in some local jurisdictions. Thus, in keeping with the intent of this paper to be a practical guide for decision-makers, reference is made to safety-related considerations and the restrictions which may be imposed by some states or municipalities on CNG vehicle operation.