Aother key factor affecting weekly variations in product supply estimates is the impact of timing on respondents’ WPSR reporting. All WPSR respondents are instructed to report their weekly activities, including pipeline/terminal product inventories as well as imports, refinery operations, blending activities, and ethanol production, as of Friday at 7:00 a.m. Eastern Time. For imports in particular, it is easy to see how an incoming vessel that just misses clearing U.S. customs by EIA’s Friday 7:00 a.m. reporting deadline can affect the product supplied estimates for a given week.
In this hypothetical case, assume a vessel bringing in 300,000 barrels of gasoline is scheduled to arrive Friday morning during Week 1, but is delayed by fog and does not clear customs until 7:05 a.m. Since this vessel did not meet EIA’s Week 1 reporting deadline, it would not be included in that week’s gasoline product supplied estimate, but would instead be included with imports that determine gasoline product supplied during Week 2. The impact of this five-minute delay (along with any other vessels arriving on Friday shortly after 7:00 a.m.) would lower gasoline product supplied in Week 1 and raise it in Week 2. During weeks when a number of vessels arrive either just before or just after the weekly reporting deadline, week-to-week product supplied estimates can swing more wildly than might be expected. Again, using a two-week or longer moving average would give WPSR users a more complete context for reviewing the product supply situation over the relevant period. This is why the WPSR includes four-week moving averages for many of the statistics, including product supplied.
The examples above highlight the peril of attempting to draw overly broad conclusions based on changes from one week to the next in the WPSR weekly petroleum product supplied estimates. While every week’s data adds to the set of relevant and important information for discerning market trends, one week’s report, by itself, is not sufficient to distinguish between the beginning of a new trend, the end of an existing trend, or simply a one-week anomaly. Similar to the deeper understanding that comes when we step back from an impressionist painting whose details we may have been focusing on too intently, the WPSR’s fuller image often comes into clearer view when we examine the broader picture.
Source: U.S. Energy Information Administration