I did a quick search and found this article from Oct 2006.
The Age Blogs: Travel
So 2 years ago QF had the levy at $31 a domestic leg whilst the article states, "
oil prices have slid to around $59 a barrel compared with $70 earlier in the year."
Article also states that "Virgin Blue's fuel levy has remained unchanged since April 2005."
So 2 years later, oil prices have slid to under $59 a barrel.
?