Контекст:
The IPE Brent Index is calculated as an average of the following elements:
............
2. Second month trades in the 21 day BFO market plus or minus a straight
average of the spread trades between the first and second months.
3. A straight average of all the assessments published in media reports.

если еще кто-то подскажет, что означает:
a straight average of the spread trades - будет просто сказка! :)