Last week I reported that their OPS relative to the league average was just 81. If that is what they finished with, it would be the lowest ever. This is what I said last week: "They have a team OPS of .597 while the NL average is .735. So they have a rate of 81 (.597/.735 = .81, which is 81 when multiplied by 100)." (actually .8122)
But now their OPS is down to .590 while the league OPS is .733. The ratio is now .8049, just a little lower than a week ago. Last week's post Astros Offense On Record Setting Low Pace shows the worst 10 teams in both AL and NL history.
But this is not park adjusted. Baseball Reference has OPS+, which is park adjusted. It is calculated a little differently. Here is the formula:
100*[OBP/lg OBP + SLG/lg SLG - 1]
The Astros now have an OPS+ of 58. See this Baseball Reference link. The lowest team OPS+ I found going all the way back to 1920 was 69 for the 1920 Philadelphia A's.