10 CFR §217.31

1. (a)Levels of priority.
   1. (1)There are two levels of priority established by the Energy Priorities and Allocations System regulations, identified by the rating symbols “DO” and “DX”.
   2. (2)All DO-rated orders have equal priority with each other and take precedence over unrated orders. All DX-rated orders have equal priority with each other and take precedence over DO-rated orders and unrated orders. (For resolution of conflicts among rated orders of equal priority, see § 217.34(c).)
   3. (3)In addition, a Directive regarding priority treatment for a given item issued by the Department of Energy for that item takes precedence over any DX-rated order, DO-rated order, or unrated order, as stipulated in the Directive. (For a full discussion of Directives, see § 217.62.)
2. (b)Program identification symbols. Program identification symbols indicate which approved program is being supported by a rated order. The list of currently approved programs and their identification symbols are listed in Schedule 1, set forth as an appendix to 15 CFR part 700. For example, DO-F3 identifies a domestic energy construction program. Additional programs may be approved under the procedures of E.O. 12919 at any time. Program identification symbols do not connote any priority.
3. (c)Priority ratings. A priority rating consists of the rating symbol—DO or DX—and the program identification symbol, such as F1, F2, or F3. Thus, a contract for a domestic energy construction program will contain a DO-F3 or DX-F3 priority rating.