Last minute fares on United's PHL-IAH are quite expensive. Of course, it's the summer - peak season, but if I want to fly any day next week on a nonstop, and book a one-way, it's $718, on any of UA or AA's nonstops. WN doesn't price competitive out of PHL to HOU. One has to look at BWI. For those that don't want to trek to BWI or EWR, but originate from PHL - F9 should be able to profitably fill seats on the westbound when UA and AA have a highway robbery fare. F9's return is an uncomfortable red-eye, with a 4am arrival in PHL. The fare for this Wednesday night (8/1) is $39. But, F9 operates a daytime AUS-PHL and it's fares are higher and likely performing well. The SAT-PHL flight was an early flight, but it appears to be changing to a late afternoon flight in August.

One has to book much in advance to get United's Basic Economy. On my ACY-MSY flight, I think there were a number of passengers who were connecting to DFW and the flight was 90-95% full. I don't know if it makes it profitable, but many of Spirit's flights are connection friendly to a few markets. e.g. if I go on Spirit's site, and check ACY to DFW, there are typically 2 decent 1 connection flights and fares under $150 on most days to stimulate some travel between the markets. With F9's website and network out of PHL and TTN, it's almost impossible to find one stop itineries aside from DEN connections.