If a market is rallying, the volume oscillator should rise.
When the issue becomes overbought, the oscillator will reverse its direction.
If the market is declining or moving in a horizontal direction, the volume should contract.
It is important to note that an increasing price, together with declining volume, is always, without exception, bearish.
When the market is at the top, one would therefore see an oversold volume chart.
Another important fact is that rising volume, together with declining prices, is also bearish.