The company would not comment. Buyers said plants for both products in La Porte, Texas, are operating at reduced levels.
Allocations set by the producer call for VAM customers to receive 80% of their average monthly purchase, and acetic acid customers to get 70% of their average purchase, buyers said.
LyondellBasell declared force majeure on VAM in March. The acetic acid declaration occurred earlier this month.
All of the major US VAM producers have experienced a supply squeeze this year, partly because of US maintenance and plant problems and also because of plant closures in the UK and Spain in late 2013.
In late May, sources said LyondellBasell's 544,000/tonne acetic acid unit in La Porte had gone down because of problems getting carbon monoxide (CO) delivered.
The company sent a letter to customers on 10 June saying it was declaring force majeure on both acetic acid and VAM because of utilities and feedstock supply disruptions. Acetic acid is a major VAM feedstock.