Frank
Well, 1100 kgs would equate to 30 minutes reserve fuel as an average. Add to that diversions fuel of about another 800 kgs (very much variable dependent on where you are - anything from 500kgs to 3000kgs) - lets go with 800 kgs. That totals 1900 kgs - add to that contingency unused at 15 minutes = 600 kgs and it totals 2500 kgs or there abouts.