Diesel Generator vs. Gas Generator: Which is More Efficient?

If you're considering a  commercial backup generator for your business, you'll have a lot of decisions to make. One of the first things to consider is the fuel source. One common question is, are diesel generators better than gas?

The answer is, it depends on the needs of your business. To help make your choice, you will need to consider your business requirements, the location of your facility and the availability of the fuel types. In this post, we’ll explore how fuel efficiency impacts your generator cost of ownership performance, and what other factors you should consider when selecting a generator.


How Efficient are Diesel Generators?

Diesel generators are known for their efficiency, and the reason is simple: Because diesel generators use compression to ignite fuel, they do not need to use as much fuel to operate as a natural gas generator. Diesel generators introduce and compress air and fuel into the engine separately, which allows them to use less fuel for power output.

Typically a diesel generator will run at about  40 percent efficiency in its designed optimum operating range, usually up to 80 percent of total load capacity. That means for every 100 units of energy input, 40 units are delivered as output. As in any mechanical system, there are energy losses from heat and friction.

For a diesel generator, efficiency can be expressed as  specific fuel consumption on a gallon-per-hour basis. Manufacturers usually provide this information in their marketing materials. You can use the SFC number as one consideration when you're deciding which generator to buy.

Are Natural Gas Generators Efficient?

Diesel fuel has about three times greater peak energy density than natural gas, or generally 129btu versus 37btu. Consequently, even the most efficient natural gas generators can’t yet beat diesel generators in terms of efficiency.

However, fuel efficiency isn’t the only consideration you should have in mind when selecting a generator. Depending on your application and power needs, certain benefits of a natural gas generator may be desirable, including their tendency to be quieter and more eco-friendly.

Which Other Factors Should You Consider?

Many factors will help you decide whether a diesel or natural gas generator is right for your situation, including fuel efficiency. It’s important to weigh all the pros and cons of diesel vs. natural gas generators before making a selection, and carefully considering how each fit into your overall power generation needs.

Here's a look at some of the top considerations when trying to determine whether diesel or gas generators best suit your needs.

Diesel Gas


Diesels typically have a better efficiency rating than gas generators. You get more energy per dollar using diesel fuel.

Gas generators are not as efficient. While natural gas is usually inexpensive, it doesn't carry as much energy.


Diesel is widely available, but weather events could impact delivery. On-site storage is crucial for long term operation.

Natural gas is usually available in populated areas but supply may be shutoff during localized events. It also may not be available in remote areas. You may have to bear the cost of running supply lines.


Regular maintenance is critical to maintaining efficiency and lower emissions. Maintenance on a diesel engine is less expensive than a comparable gas engine.

Natural gas engines may have higher maintenance costs due to using spark plugs and wires.


Diesel engines, especially those that are rarely used, can last for a very long time – even decades – with regular maintenance.

A gas engine won't last quite as long as a diesel, but regular maintenance will help.


Diesel fuel is less flammable than other fuel types, and the lack of spark plugs reduces the risk of fire. Installations must include spill a containment basin in case the fuel leaks.

Natural gas is extremely flammable in the case of a pipeline leak. Manufacturers are improving their enclosures for increased fire safety.


While diesel engines do produce higher amounts of pollutants than gas generators, new diesel units that meet EPA regulations are much cleaner.

Natural gas emits much lower levels of sulfur, nitrogen, and carbon dioxide than diesel. It does not produce an odor when it burns.

Get Help With Your Generator Selection

Recent improvements to both diesel and natural gas generators means that the performance gaps between the two have narrowed significantly. Today, diesel fuel generators emit much less pollution than their predecessors, and many natural gas generators can meet operating requirements previously met only by diesel generators. Choosing between these two types of generators is easiest when working with an experienced power expert that understands how these recent advancements impact generator performance.

At  General Power, our experts can help you understand which type of generator is best for you based on your location, industry, power needs and budget. If you need help with generator selections, get immediate assistance by calling our team at  1-888-819-5646.