It depends how you classify low volume. I can see two big bars on the Bitfinex 24 hour chart, and each of them is above 1000 Bitcoins and mostly buying.
Is buying possible without selling?
No but if the ask side gets eaten into it's considered buying and selling if the bid side gets eaten into.
Ah, gotcha. How does one tell if the ask side got eaten into by looking at the volume bars?
It's hard to say. Generally you would assume that green bar means buying and red bar means selling but it's not always that simple.
Let's say the price is 664.5 and the ask side is just 1 btc to get to 665 so somebody buys 1 btc and the price is now 665 then say somebody puts up a bid wall at 664.8 for 100 btc and 90 of those goes through.
So now the price is 664.8 and 1 btc has been bought and 90 has been sold but the chart still shows that 91 btc has been bought.
I don't pay attention to volume a lot though so somebody else could perhaps clarify it further.