Citations are to the 20th edition of The Bluebook, A Uniform System of Citation
Code of Federal Regulations (1938-date): x C.F.R. § x (year). Notice here that there is only a year in the parenthetical.
BOOK VERSION: 31 C.F.R. § 100.5 (2012). The most recent volume of the C.F.R. with this section in it is from 2012.
WESTLAW: 31 C.F.R. § 100.5 (Westlaw 2014).
LEXIS ADVANCE: 31 C.F.R. § 100.5 (Lexis Advance 2014).
The complete archive of the C.F.R. is found on Heinonline in the Federal Register Library.
Federal Register (1936-date): vol. no. Fed. Reg. page number (month, day, year).
EXAMPLE: 37 Fed. Reg. 23,603 (Nov. 4, 1972).
EXAMPLE of Four-digit page number: 79 Fed. Reg. 3481 (Jan. 22, 2014).
Page number is subject to R6.2(a)(vii): In numbers containing five or more digits, use commas to separate groups of three digits in the page number for the Federal Register.
The complete archive of the Federal Register is found on Heinonline in the Federal Register Library.