The US liquid quart is a unit of volume in the US customary system with the symbol qt.
The US liquid quart is equal to 1/4 US liquid gallons, 2 US liquid pints, 4 US liquid cups, 8 US liquid gills or 32 US fluid ounces. The SI / metric equivalent is ≈ 0.946353 L.
The US liquid quart was based on exactly 57.75 in³ which was derived from the 1959 international yard and pound agreement whereby all traditional length and volume measures were legally standardised.
The barrel is a unit of volume used in the oil industry with the symbol bbl.
Oil is more commonly expressed in terms of cubic metres (m³) but in the US and in the economic world (mainly because such a large percentage of the world's oil is shipped to the US) as barrels.
The measurement of the barrel originated in the US at the first oil well in Pennsylvania. There were so many variants of barrel size (including those used for wine and other goods) that the distrust became so prevalent a central and standard barrel size was created. This was finally established in 1872 as 42 US gallons.