UPDATE: As of Friday night, Delta matches United’s airfare hike.

EARLIER: We had almost 2 months of calm from system-wide legacy airline hikes, until last night - when United Airlines initiated the 22^nd attempt of 2008.

The carrier increased airfares up to $20 roundtrip, on the bulk of its route system, affecting both leisure and business travelers. Curiously, the increase comes amidst 3 weeks of very active leisure ticket discounting for travel through mid-November.

Capacity cutbacks begin in earnest starting after Labor Day and I had expected to see some hikes a bit earlier to correspond with these cuts - it appears however that consumers benefited from the drop in oil prices from $147 to $115 a barrel since early July. But that’s changing.

Our laboratory beta “Best Time to Buy Technology” showed the following United price graph comparing the cheapest roundtrip prices at noon Thursday, to the newly hiked prices of last night between the top 50 cities (1200 markets):

Note the graph highlights United pricing behavior:

• Cheaper prices through end of October
• Price increase for Thanksgiving Travel in Mid November
• Price increase for Christmas Travel in Mid December
• Huge price increase for those that book outside the Southwest airlines booking window which ends in early March.

NOTE: Air travelers should not procrastinate on holiday travel this year as we are likely to see a few more hikes before the end of the year.

And for a look back at the year’s hikes by all the airlines, see our 2008 Airfare Hike Timeline Chart.