The Gasoline Gap: How California’s Biggest Emissions Source Is Falling Behind

This is the second in a series of articles examining California’s progress toward the greenhouse gas (GHG) reduction targets set by the 2022 Scoping Plan. The first article – Mind the Gap: Transportation Emissions vs. California’s 2022 Scoping Plan Pathway – provided background and an overview of how the transportation sector has performed in reducing GHG emissions relative to the 2022 Scoping Plan pathway.^[1] This second article focuses on how the trajectory of gasoline emissions is tracking versus the 2022 Scoping Plan.  

Bottom Line Up Front: GHG emissions from gasoline are declining, but at a slower pace than the 2022 Scoping Plan projects. The three key drivers impacting results are the number of gasoline-powered vehicles on the road, the total annual vehicle miles traveled (VMT), and the average fleet fuel economy.

 

Gasoline Fuel Use and GHG Changes through 2025

California’s population growth from 1950-2000 was the primary historical driver of rising gasoline demand. In recent years, however, population growth has plateaued and, in some periods, declined, contributing to a leveling off in fuel use. Figure 1 illustrates California’s gasoline demand over time. As can be seen, prior to 2004, demand followed a steady upward trend; the dotted line projects where that trend would have led absent any changes in conditions. After 2004, the pre-existing trend broke, reflecting a series of significant shifts:  

1. The implementation of AB 32 in 2006,  
2. Sustained higher gasoline prices,  
3. The 2007-2009 economic recession,  
4. Electric vehicle (EV) sales rising to significance,  
5. The start of stricter EPA fuel economy standards in 2010, and  
6. The COVID-19 pandemic’s sharp reduction in driving.  

More recent net outmigration of higher-income residents – who tend to drive more – has also contributed to reduced demand. By 2025, California’s gasoline sales volume returned to approximately 1990 levels. EV adoption has displaced about 6.4% of gasoline use.  

Figure 1. California Gasoline Fuel PerspectiveSource: Stillwater Analysis of Board of Equalization and LCFS Quarterly Data Summary  

GHG emissions from gasoline vehicles are directly tied to fuel use, which is influenced by the number of vehicles on the road, VMT, and fuel efficiency (miles per gallon or MPG). Fuel prices strongly influence VMT and consumers’ decisions to buy more fuel‑efficient vehicles. In fact, Stillwater’s analysis finds that most GHG reductions from 1990 to 2025 stem from lower VMT and increased purchases of fuel‑efficient vehicles in response to higher gasoline prices.  

Figure 2 compares historical gasoline GHG emissions through 2025 against the 2022 Scoping Plan trajectory. The Scoping Plan anticipated a stronger rebound toward pre-COVID fuel consumption (and emissions) by 2022, but continued remote work and shifts in consumer behavior – such as increased online shopping – kept gasoline demand below that projection. California’s AB32 policies – including the Low Carbon Fuel Standard, LCFS – are also contributing to gasoline GHG reductions. Beginning in 2023, actual emissions crossed above the Scoping Plan projection. Stillwater’s analysis finds that 2025 gasoline GHG emissions are approximately 10.6% higher than the Scoping Plan projection. If this trajectory holds, by 2030, actual emissions will be significantly higher than the Scoping Plan estimate. The divergence reflects the Scoping Plan’s more optimistic assumptions about EV penetration, fuel economy improvements, and VMT reductions. 

Figure 2. Historic Gasoline Vehicle and Scoping Plan GHG EmissionsSource: Stillwater Analysis of AB 32 GHG Inventory Sectors Modeling Data Spreadsheet from Final 2022 Scoping Plan Update and Appendices, and LCFS Quarterly Data Summary Spreadsheet

 

Vehicle Miles Traveled (VMT)

Figure 3 compares historic light-duty vehicle (LDV) VMT with the Scoping Plan’s projected VMT trajectory. The gap between actual and projected VMT mirrors the GHG emissions divergence seen in Figure 2. The Scoping Plan calls for a 26% reduction in statewide LDV VMT from 2024 levels by 2030 – a larger decline than the 13.5% drop in VMT observed at the height of the COVID-19 pandemic. 

Figure 3. Historic vs Scoping Plan Light Duty Vehicle VMTSource: Stillwater Analysis of AB 32 GHG Inventory Sectors Modeling Data Spreadsheet from Final 2022 Scoping Plan Update and Appendices, and Stillwater Analysis, modeling LCFS fuel sales, CEC Populations, EPA Fuel Economy Data

The number of gasoline-powered vehicles on the road is another key driver of fuel consumption. Stillwater’s analysis identifies a 7% difference between the LDV population estimates used in the Scoping Plan (based on CARB’s EMFAC model) and data from the California Energy Commission (CEC), which is derived from vehicle registrations. For the analysis presented in this article, we have accounted for these source differences. Figure 4 compares gasoline LDV population estimates from both sources, along with the total LDV fleet including EVs and other ZEVs. The CEC data indicates that the number of gasoline-powered LDVs has grown faster than the Scoping Plan projected, and the gap between the two estimates appears to be widening. 

Figure 4. Light Duty Gasoline Vehicle Stock ComparisonSource: Stillwater Analysis California Energy Commission Vehicle Populations and 2022 Scoping Plan Model Data (2022 Scoping Plan Model Data / LDV Stock)

 

Comparing LDV Fuel Economy

As shown in Figure 5, historical fuel economy data for gasoline-powered LDVs through 2025 suggest that the Scoping Plan’s assumptions were optimistic. The Scoping Plan projects a 32% improvement in fleet fuel economy over 12 years, compared to the 14% improvement observed over the preceding 12 years. This trajectory is difficult to reconcile with the well-established pattern of diminishing returns in fuel economy technology: the largest efficiency gains typically come early in an improvement cycle, with incremental gains becoming harder to achieve over time. California’s recent fuel economy trend already reflects this dynamic, with gains beginning to plateau. Additionally, fleet-wide improvement is inherently gradual – with approximately 22 million registered vehicles on the road and new vehicle sales comprising only about 7% of the fleet annually, full fleet turnover takes roughly 12-15 years. 

Figure 5. Gasoline LDV Fuel Economy – Scoping Plan and HistoricSource: Source: Stillwater Analysis of AB 32 GHG Inventory Sectors Modeling Data Spreadsheet from Final 2022 Scoping Plan Update and Appendices, and Stillwater Analyis of The EPA Automotive Trends Report | US EPA and News – California New Car Dealers Association Quarterly Auto Outlook

 

Reaching the LDV GHG Goal

As noted in the first article in this series, transportation accounts for 37% of California’s statewide GHG emissions. Of that transportation total, gasoline accounts for approximately 82% – making gasoline GHG emissions (primarily from LDVs) roughly 30% of all statewide GHG emissions. Given the state’s goal of a statewide 85% reduction from 1990 GHG levels by 2045, meaningful progress on gasoline emissions is essential. Figure 6 illustrates the GHG emissions of various fuel and vehicle technology combinations. The comparison illustrates that pathways to significant GHG reduction from LDVs are limited. Of the fuel and vehicle technology combinations shown, only plug-in hybrid electric vehicles (PHEVs) and conventional hybrid vehicles fueled with E85 and battery electric vehicles (BEVs) powered by renewable electricity would deliver an 85% reduction in GHG emissions compared to gasoline.[2] Notably, EVs charged on California’s current grid mix achieve considerably smaller reductions than EVs charged entirely on renewable power — underscoring that decarbonizing electricity generation is a prerequisite for maximizing the GHG benefit of EV adoption.  

Figure 6. Vehicle GHG Emission Technology Options Source: Stillwater analysis of 2022 Scoping Plan model data.  

Note: In this figure, EV represents BEVs, hybrid represents conventional gasoline hybrid vehicles, and ICE represents conventional internal combustion engine vehicles.

 

Conclusion

Several years into the 2022 Scoping Plan period, gasoline emissions and the variables that drive them – VMT, fuel economy, and vehicle stock – are not on the trajectory the Scoping Plan projected. The Scoping Plan initially overestimated the post-COVID recovery in gasoline demand, which kept actual emissions below projections through 2023. But beginning in 2024, actual gasoline GHG emissions crossed above the Scoping Plan projected pathway. With gasoline accounting for approximately 30% of California’s total statewide GHG emissions, the gap between actual performance and the Scoping Plan trajectory has significant implications for California’s long-term climate goals. The limited pathways to substantial gasoline GHG reductions through 2045 – primarily E85 in flex-fuel vehicles, PHEVs, or BEVs powered by renewable electricity – reinforce the scale of the challenge ahead.  

Stay tuned for the next installments of this series: Part 3 will examine diesel fuel GHG emissions versus the Scoping Plan, Part 4 will assess electric vehicle trends and ZEV adoption progress, and Part 5 will offer a comprehensive wrap-up of California’s transportation GHG trajectory relative to the 2022 Scoping Plan.