Prices Are From 15Th Of Month. Source: For 1918-1925, Furnished Directly By Bls. For 1926 On, From Bulletins Beginning With No. 473.
This NBER data series m04132 appears on the NBER website in Chapter 4 at http://www.nber.org/databases/macrohistory/contents/chapter04.html.
NBER Indicator: m04132
Release: NBER Macrohistory Database
National Bureau of Economic Research, Wholesale Price, Asphalt (Bulk, Tank Cars, Refinery) for United States [M04132USM299NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/M04132USM299NNBR/, July 7, 2015.