Emissions data: CO₂ emission factors used in this calculator (gasoline: 2.32 kg/L, propane: 1.51 kg/L, diesel: 2.68 kg/L) are sourced from the
EPA eGRID Database and
U.S. Energy Information Administration (EIA) fuel emissions coefficients.
Generator Fuel Cost Comparison Guide
Gasoline — The Most Common Choice
Gasoline is the most widely available generator fuel, and consequently the most common choice for portable generators. However, gasoline has significant drawbacks for emergency preparedness: it degrades in 30 days without stabilizer, it is difficult and hazardous to store in large quantities, and during regional emergencies (hurricanes, ice storms), gas stations frequently run out of stock. Furthermore, gasoline-powered generators emit significantly more CO than propane, increasing the hazard from accidental indoor operation. A 5,500W generator running at 50% load consumes approximately 0.5–0.7 gallons per hour — requiring 20–30 gallons for a 72-hour outage at 10 hours/day of operation.
Propane — Superior for Emergency Storage
Propane stores indefinitely in sealed tanks, making it substantially more reliable than gasoline for emergency preparedness. A 100-pound propane tank holds approximately 23 gallons of liquid propane, providing roughly 60–75 hours of operation for a 5,500W generator at 50% load. Additionally, propane starts more reliably in cold weather than gasoline — a significant advantage in ice storm scenarios where generators are most needed. However, propane tanks require special handling, cannot be filled to 100% capacity (maximum 80% fill), and require proper ventilation during generator operation.
Natural Gas — The Standby Generator Advantage
Standby generators connected to natural gas utility lines offer unlimited runtime — the only fuel source that can sustain a whole-home generator through a multi-week outage. Natural gas is also the most cost-efficient fuel per kWh of generator output in most US markets. However, natural gas infrastructure can be disrupted by the same major disasters (earthquakes, floods) that cause extended power outages. Furthermore, the gas line must have sufficient flow capacity for the generator's peak consumption — a licensed gas plumber must verify this during installation.
Diesel — The Commercial Choice
Diesel offers the highest energy density per gallon of any common generator fuel, resulting in the longest runtime per tank. Diesel generators are, therefore, the dominant choice for commercial standby applications where reliability and efficiency are paramount. For residential use, however, diesel is less common due to higher generator purchase prices, the need for proper fuel tank installation for storage, and less availability in smaller portable generator formats. Additionally, diesel fuel gels in extreme cold (below approximately -20°F / -29°C), requiring fuel additives in northern climates.