Economics
Secondary Market Liquidity and Bid-Ask Spreads
Quick fact
The bid-ask spread can be as small as a penny for highly liquid stocks like Apple, but can be several percentage points for thinly traded bonds or small-cap stocks.
Why this is interesting
You want to sell a stock you own, but the price you see isn't exactly what you'll get. Why does it cost more to trade some investments than others?
Read the full explanation
Understanding Secondary Market Liquidity and Bid-Ask Spreads
Imagine you're at a flea market wanting to sell a vintage watch. A dealer might offer you $50 (the bid), but a buyer looking to purchase might see the watch priced at $70 (the ask). The $20 gap is similar to a bid-ask spread. In financial markets, the bid is the highest price a buyer is willing to pay, and the ask is the lowest price a seller will accept. The difference is the bid-ask spread. This spread is the compensation for market makers—the intermediaries who provide liquidity by standing ready to buy or sell. They profit from the spread, and the size of the spread reflects the risk they take and the liquidity of the asset.
A deeper explanation
Secondary market liquidity is the ease with which an investor can trade an asset without causing a significant price change. High liquidity means many buyers and sellers, or 'depth,' allowing large trades with minimal impact. Low liquidity means fewer participants, wider spreads, and more price volatility. The bid-ask spread is the primary visible measure of liquidity. Market makers set bids and asks based on their inventory risk and adverse selection risk. If a stock is frequently traded with many informed traders, the market maker faces greater risk of trading with someone who knows more, so they widen the spread to protect themselves. Conversely, for heavily traded blue-chip stocks, the risk is lower, allowing a tight spread. This spread directly affects investors: it's a hidden transaction cost, as you buy at the ask and sell at the bid, effectively losing the spread on a round-trip trade. Understanding this helps investors compare costs across assets and recognise why illiquid assets must offer higher returns (liquidity premium). It also explains how electronic trading and high-frequency market makers have narrowed spreads, reducing costs for investors but potentially changing market dynamics.