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It can be closed. You could forget about it for a year, then claim the entire year's Gas at that point. As long as you hold NEO in the wallet, you are earning Gas.

Does the amount of neo you have in the wallet correlate with the amount of gas accumulated or does it accumulate the same for all?

The more NEO you have the more GAS you'll earn. I think if you had 1 NEO, it will take 22 years to collect 1 GAS, so if you had 2 NEO, that number will drop to 11 years and so on...

WOW! This is a valuable piece of info. Thank you. So can you claim any fractional gas past for decimals? Or just leave it and let it build.

@athoughtbytim You can claim GAS at any time. The only thing that affects the amount of GAS generated is how much NEO you have on your private wallet. If you want to simulate how much GAS your current NEO will give you go to neotogas.com.