Other data types (open interest, spreads, and more)
A clear intro to the data beyond price and volume: the bid-ask spread, open interest, liquidity, and gaps, and what each one adds when you read a chart.
Part of the Reading the Market: Charts and Data track on Agenticks. About 8 minutes, written for a beginner reader.
So far this track has focused on the two things almost every chart shows: price and volume. Price tells you where the market traded. Volume tells you how much trading happened. That is a strong foundation, and for a lot of charts it is all you need. But markets produce more numbers than just those two. Sit next to the price of a futures or options contract and you will see a few other data points: the bid and the ask, the spread between them, open interest, and a sense of how much liquidity is around. None of these replace price. They sit beside it and answer questions price cannot answer on its own.
Start with the bid and the ask. At any moment there is a highest price a buyer is willing to pay, called the bid, and a lowest price a seller is willing to accept, called the ask. They are almost never the same number. The gap between them is the spread. The spread is a real cost. If the bid is 100.00 and the ask is 100.05, you buy at 100.05 and could only immediately sell at 100.00. You are down a nickel before price moves at all. In a busy, heavily traded market the spread is tiny. In a quiet or thinly traded one it can be wide, which means it costs more just to get in and out.
A tight spread is a sign of liquidity
Liquidity is how easily you can trade size without pushing the price around. When a market is liquid there are lots of buyers and sellers stacked close together, so the spread is narrow and you can enter or exit near the price you saw. When liquidity dries up, the spread widens and fills can land further from where you expected.
Now to a number that is easy to mix up with volume: open interest. It only exists for contracts like futures and options, not for plain stock. Volume counts how many contracts changed hands during a period. Open interest counts how many contracts are currently open and have not been closed out yet. The difference matters. Imagine 100 contracts trade today. If those trades are mostly people opening brand new positions, open interest rises. If they are mostly people closing existing positions, open interest falls, even though volume was the same 100 either way. A simple way to hold the two apart: volume is the activity during the period, open interest is the pile of positions still standing at the end of it.
On a futures contract, today's volume was 500 contracts and open interest fell from 2,000 to 1,900. What does that tell you? More positions were closed than opened during the day Right. Volume measures the activity, while a drop in open interest means the day's trading closed more existing positions than it opened.
A few other data points show up once you look beyond a single chart. A gap is an empty space where price jumps from one candle's close straight to the next candle's open, with no trading in between. Gaps often appear after hours, when news lands while the market is closed and it reopens far from where it left off. Markets that trade around the clock show fewer gaps. There are heavier datasets too, like the order book, which lists the resting buy and sell orders waiting at each price, and order flow, which tracks the trades hitting the bid and the ask in real time. Those are their own topic for later. For now the point is simply that price and volume are the start, not the whole picture.
- Volume
- How many shares or contracts traded in a period
- Open interest
- How many contracts are still open and not closed out
- Spread
- The gap between the bid and the ask
- Liquidity
- How easily size trades without moving price
- Gap
- Empty space where price jumps with no trading in between
Extra data is context, not a replacement
None of these numbers tell you what price will do next, and none of them replace the chart. They add context. The spread tells you what trading costs right now. Open interest tells you how committed a futures or options market is. Liquidity tells you whether your fill will land near the price you saw. You still read price first, then let the rest fill in the picture.
spread liquidity open interest
You can read beyond price and volume
You now know what the bid-ask spread costs you, how open interest differs from volume, what liquidity describes, and that a gap is a jump with no trading in between. Each one is context that sits beside price, not a replacement for it.
Common questions
- What is the difference between volume and open interest?
- Volume counts how many contracts or shares traded during a period. Open interest counts how many futures or options contracts are still open and have not been closed out yet. Volume measures activity; open interest measures positions that currently exist.
- What is the bid-ask spread?
- The bid is the highest price a buyer is currently willing to pay and the ask is the lowest price a seller will accept. The spread is the gap between them. A wider spread means it costs more to enter and exit a position.
- Do I need all this extra data to read a chart?
- No. Price and volume are enough to start. The bid, the ask, open interest, and liquidity are extra context that becomes useful as you study specific markets like futures and options, where these numbers explain things price alone cannot.
Terms defined in this lesson
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