Virginia now has an official count of the machines that keep its data centers running when the grid fails. A report delivered to the General Assembly's money committees on October 1, 2026 by the staff of the State Corporation Commission (SCC), compiled with the Department of Environmental Quality (DEQ), lists 10,290 permitted Tier 2 (or earlier) generator sets at data centers with a combined capacity of 26,718 MW, and 3,477 Tier 4 or Tier 4-equivalent sets with 6,414 MW. In total, that is 13,767 generators and 33,132 MW of backup capacity, almost all of it fueled by diesel.
The count arrives as diesel prices in the US have climbed to levels not seen since 2022, driven by the conflict that closed the Strait of Hormuz at the end of February.
Backup that exceeds the load
The same report, required by the 2026 budget bill, gives the first aggregated figure for contracted data center demand across Virginia's utilities. Electric service agreements or equivalent contracted demand with data centers total 11,997 MW at Dominion Energy Virginia, 7,513 MW at Northern Virginia Electric Cooperative, 898 MW at Mecklenburg Electric Cooperative, 842 MW at Rappahannock Electric Cooperative and 541.4 MW at Appalachian Power. That adds up to 21,791 MW.
The permitted generator fleet is about 1.5 times that contracted load. That ratio reflects how data centers are designed. Operators build redundancy so that a facility can keep running if one or more generators fail to start. DEQ's January 2025 air permit guidance for data centers notes that Northern Virginia facilities have "predominantly employed Tier II diesel engine driven generator sets for backup power," typically classified as emergency units, and it recommends redundancy with cleaner Tier IV units as primary backup and Tier II units for emergency-only use.
Part of the gap also reflects timing. Generators are permitted when a facility is built, while contracted load may ramp up over several years. And some permitted generators may serve capacity that is planned but not yet under contract.
The Hormuz diesel shock
The war that began on February 28 created what the International Energy Agency (IEA) calls the largest supply disruption in the history of the global oil market. The IEA says the price of diesel "has nearly doubled in the United States compared with pre-war levels."
Weekly retail data from the Energy Information Administration (EIA), compiled by the Federal Reserve Bank of St. Louis, show the US average on-highway diesel price at $3.809 a gallon in the week of February 23, 2026. It passed $5 in mid-March, eased to $4.578 in early July after the interim US-Iran agreement, then climbed again to $6.529 in the week of September 21 and $6.382 in the week of September 28. That is about 68% above the pre-war level.
Diesel at a data center is mostly a standby cost. Generators run for short periods of maintenance and readiness testing, and otherwise sit idle with fuel stored on site. But the fuel has to be bought, rotated and replaced, and a generator fleet the size of Virginia's makes even standby costs material.
What a full run would cost
A common rule of thumb in the generator industry is that a diesel set burns roughly 0.07 gallons per kWh at full load. On that basis, Virginia's 33,132 MW of data center generators would consume about 2.3 million gallons an hour if all ran at full output at once. At $6.38 a gallon, that is close to $15 million an hour.
That is an illustrative ceiling, not a forecast. Generators would never all run at full load at once, because they are sized with redundancy and data centers rarely operate at their full contracted demand. But the arithmetic shows why the price of diesel matters to grid planners as well as operators. In a prolonged outage, the backup fleet becomes a large consumer of a fuel that has been at the center of the Hormuz shock.
Why grid operators care
The generator fleet sits inside PJM Interconnection, where data center demand is the main driver of rising load forecasts and capacity prices. Backup generation has been proposed in various forms as a resource that could help the grid during emergencies, by allowing data centers to disconnect and run on their own power when supply is tight.
The air permits complicate that idea. DEQ's guidance distinguishes between emergency generators, which face operating limits, and non-emergency units fitted with controls such as selective catalytic reduction, which can run more often but must stay below major source levels. A Tier II emergency unit is listed in the guidance with a much higher NOx emission rate than a Tier IV or controlled unit. Using backup generators to support the grid on a regular basis would mean running mostly older, dirtier units, in a region already subject to air quality limits.
The Virginia count shows that three-quarters of the backup capacity is Tier 2 or earlier: 26,718 MW out of 33,132 MW. Converting that fleet to cleaner units would be expensive, and higher diesel prices add to the cost of running it at all.
Water data still missing
The report was also meant to quantify data center water use. It could not. No responding regulated water utility identified itself as serving data centers, and responses from municipal utilities were not received in time. DEQ is building a public dashboard of water withdrawal and use data, including for data centers, with a go-live date of January 1, 2027.
What it means
Virginia's first aggregated numbers give a clearer picture of the scale of its data center industry: about 21.8 GW of contracted load and about 33.1 GW of backup generators. The Hormuz crisis has added a cost that few expected to matter, because backup fuel is usually an afterthought next to electricity.
The larger lesson is that data centers are not only electricity customers. Through their backup fleets, they are also among the largest holders of diesel-fired generating capacity in the PJM region, and their exposure to oil markets is larger than their electricity bills suggest.