Prices for both diesel and gasoline continues to fall in the U.S. this week, according to data tracked by the Energy Information Administration (EIA), while the cost of diesel exhaust fluid (DEF) critical to the proper functioning of selective catalytic reduction (SCR) emission control technology on heavy trucks remained relatively stable.

The U.S. average retail pump price for diesel dropped 2.2 cents this week to $3.897 per gallon, the agency said, which is 19.7 cents per gallon cheaper compared to the same week in 2012.

Diesel prices dropped in all regions of the country, EIA added, with New England and California reporting prices above the $4 per gallon mark, at $4.040 and $4.15 per gallon respectively, with the West Coast at a $4.052 per gallon per gallon average when California is added in (with the region reporting a $3.936 per gallon average when California is removed.)

The U.S. average retail pump price for gasoline witnessed a steeper drop, EIA noted, falling 5.8 cents this week to $3.367 per gallon – which is down 48.3 cents per gallon compared to the same week in 2012.

Where DEF is concerned, according to data tracked by international research firm Integer, the U.S. national average price for DEF tote refills remained at $1.91 per gallon while in Canada DEF prices declined a penny to CAN $0.56 per liter (roughly US $2.24 per gallon).

DEF truck stop prices increased one cent to $2.80 per gallon in the U.S. while staying flat in Canada at CAN $0.80 per liter (equating to US $3.01 per gallon), Integer added.

In other energy news, EIA also estimates that the U.S. will become the world's top producer of petroleum and natural gas hydrocarbons this year, surpassing both Russia and Saudi Arabia.

Since 2008, the agency noted that U.S. petroleum production has increased 7 quadrillion Btu, with dramatic growth in Texas and North Dakota. Natural gas production has increased by 3 quadrillion Btu over the same period, EIA added, with much of this growth coming from the eastern U.S. By contrast, Russia and Saudi Arabia each increased their combined hydrocarbon output by about 1 quadrillion Btu over the past five years.

The agency did stress that comparisons of petroleum and natural gas production across countries are not always easy, as differences in energy content of crude oil, condensates, and natural gas produced throughout these countries make accurate conversions difficult.

There are also questions regarding the inclusion of biofuels and refinery gain in the calculations as total petroleum and natural gas hydrocarbon production estimates for the U.S. and Russia for 2011 and 2012 were roughly equivalent—within 1 quadrillion Btu of one another. In 2013, however, the production estimates widen out, with the U.S. expected to out produce Russia by 5 quadrillion Btu.