Over-the-counter prices for carbon dioxide allowances under the Regional Greenhouse Gas Initiative were mixed to conclude March amid overall thin activity following the program's latest quarterly auction.

As of March 26, the March 2018 vintage 2018 RGGI CO2 allowance contract concluded its run in a bid-and-ask range of $3.83/ton to $3.95/ton, down 22 cents from the end of February.

As of March 29, the April 2018 vintage 2018 RGGI CO2 allowance contract was pegged in a bid-and-offer spread of $3.81/ton to $3.95/ton. The benchmark December 2018 vintage 2018 RGGI CO2 allowance contract was seen in a bid-and-ask range of $3.92/ton to $4.06/ton as of March 29, up 3 cents from the middle of March.

In the first RGGI auction of the year, held in mid-March, 100% of the more than 13.5 million allowances on offer were purchased at a clearing price of $3.79/ton, down 1 cent from the program's previous sale price. RGGI said 64% of the allowances sold in the March auction were bought by compliance entities or their affiliates.

The RGGI states are made up of Connecticut, Delaware, Maine, Massachusetts, Maryland, New Hampshire, New York, Rhode Island and Vermont. The nine states use a market-based cap-and-trade program to reduce greenhouse gas emissions from regional power plants, selling nearly all emissions allowances through auctions and investing proceeds in energy efficiency projects.

The March 14 auction was the first of the fourth control period. RGGI compliance is structured based on three-year control periods, the fourth of which started at the beginning of this year and will run through the end of 2020.

At the end of the control period, covered entities must provide one allowance for each short ton of CO2 emitted during the period. They also must provide allowances equal to half their emissions at the end of each interim control period, or the first two calendar years of each three-year control period.

The 2017 model rule, released in December 2017, sets a 30% reduction in regional carbon dioxide emissions between 2020 and 2030.

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