The Federal Communications Commission (FCC) is auctioning off a new round of mid-band spectrum for 5G.

Mid-band spectrum is the most coveted type of spectrum for 5G. Low-band — below 1 GHz — offers coverage on par with 4G LTE, but provides only marginally better speeds. High-band mmWave — over 6 GHz — offers speeds measured in gigabits, but has extremely limited range. Repeaters and base stations must be placed every couple of hundred meters to maintain coverage.

Mid-band, in contrast, offers speeds in excess of 1 Gbps, and provides far better coverage than mmWave. T-Mobile gained a wealth of mid-band spectrum when it purchased Sprint. Verizon and AT&T spent over $68 million at the last mid-band spectrum auction, while T-Mobile only spent $9 billion to round out its existing spectrum.

The FCC is now auctioning off a new round, specifically 100 MHz of the 3.45 GHz band. Starting Tuesday, October 5, the auction has a reserve price of $14,775,354,330 that must be met. There’s almost no chance the reserve price won’t be met, as Fierce Wireless says the final price is estimated to be $31 billion, with a reasonable chance of reaching $40 billion. Verizon and AT&T are both seen as the most likely big spenders, as both companies still have a ways to go before they catch up to T-Mobile’s spectrum holdings.

“We are moving with record speed and collaboration to free up more mid-band spectrum for 5G,” said FCC Acting Chairwoman Jessica Rosenworcel. “These airwaves are a critical part of unlocking the 5G promise everywhere in the country. I want to thank the FCC staff who have worked so hard to start this auction this year. And I want to thank our partners at NTIA and the Department of Defense for working with us to free up this spectrum for 5G.”