Table of Contents
Market Context
What Happened
Why It Matters
Sector Breakdown
Risks to Watch
What to Watch Next
Final Outlook
Market Context
At its core, a stock exchange is a marketplace where buyers and sellers come together to trade shares of publicly listed companies, with prices determined by the balance of supply and demand at any given moment. The Toronto Stock Exchange, Canada’s largest exchange and the seventh largest in the world by some measures, lists thousands of securities across a wide range of industries and trades an average of roughly 250 million shares per day. Alongside the TSX, the TSX Venture Exchange serves smaller, earlier-stage companies, offering a venue for businesses that may not yet meet the listing requirements of the senior exchange.
In 2026, algorithmic trading is estimated to account for between 60 and 73 percent of daily volume on major US exchanges, a figure that underscores how much modern markets are shaped by automated systems reacting to price movements, news, and order flow in fractions of a second. While individual investors still play an important role, understanding that a large share of daily trading activity is driven by algorithms can help explain why markets sometimes move sharply on seemingly small pieces of news, or why volatility tends to be concentrated around the opening and closing of a trading session.
For Canadian investors, understanding how exchanges function — including trading hours, how prices are set, and how different order types work — provides a useful foundation for interpreting day-to-day market movements, including the kind of broad, multi-sector reactions seen in response to major news events.
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What Happened
The past 24 hours provided a useful real-world illustration of how exchange mechanics interact with major news. Reports that the United States and Iran have reached a preliminary peace agreement broke over the weekend, while most major exchanges were closed. When markets reopened, beginning with Asian exchanges, the news was reflected immediately in opening prices, with equity indices rallying and commodity prices, particularly oil, moving sharply lower. This is a common pattern: when significant news breaks while an exchange is closed, the next opening price often reflects a meaningful adjustment from the previous closing price, sometimes referred to as a “gap” in price.
As trading continued through European and into North American sessions, including the TSX and NYSE, prices continued to adjust as more participants entered the market and additional information became available. On the TSX, this resulted in the S&P/TSX Composite Index gaining on the day, with the price-setting mechanism reflecting increased buying interest in financials and mining stocks, and increased selling pressure in energy names like Imperial Oil, as the market continuously matched buy and sell orders at prices that reflected the new information.
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Why It Matters
Continuous Price Discovery
A stock exchange functions as a continuous price discovery mechanism, meaning that the price of a stock at any moment reflects the most recent point at which a buyer and seller agreed to transact. When major news breaks, this process can happen very quickly, with prices adjusting within seconds or minutes as new buy and sell orders are placed in response to the information. For investors, this means that by the time most people become aware of major news, much of the immediate price adjustment may have already occurred, particularly for highly liquid, large-cap stocks.
The Role of Market Makers and Liquidity
Exchanges rely on market participants, including designated market makers in some structures, to provide liquidity by being willing to buy and sell shares even when there is a temporary imbalance between buyers and sellers. This liquidity provision helps ensure that prices can adjust smoothly even during periods of high volatility, such as the kind seen following major geopolitical news. However, liquidity is not unlimited, and during periods of extreme volatility, the gap between the price a buyer is willing to pay and the price a seller is willing to accept, known as the bid-ask spread, can widen.
Sector Breakdown
The mechanics of price discovery were visible across sectors in the past 24 hours. In financials, increased buying interest in TD Bank, BMO, and RBC reflected a reassessment of the outlook for Canadian interest rates following the reduction in oil-driven inflation risk, with prices adjusting upward as more buy orders entered the market relative to sell orders. In mining, names including Agnico Eagle, Barrick, and Wheaton Precious Metals saw similar upward price adjustments, reflecting broader improvements in risk sentiment even as underlying gold prices showed more modest moves.
In energy, the mechanism worked in the opposite direction: as oil prices fell sharply following the US-Iran news, sell orders for energy stocks like Imperial Oil increased relative to buy orders, and the exchange’s matching process adjusted prices downward accordingly. Meanwhile, TC Energy’s more modest price movement, despite being nominally part of the same broad energy sector, reflected how its different business model, based on long-term contracts rather than direct commodity exposure, led market participants to value it differently in response to the same underlying news.
Risks to Watch
Understanding how exchanges work also means understanding their limitations. During periods of extreme volatility, exchanges may implement circuit breakers or trading halts designed to give markets a pause and allow participants to absorb new information, though such mechanisms were not triggered by the events of the past 24 hours. For individual investors, a key risk is that the speed of modern price discovery, driven heavily by algorithmic trading, means that by the time retail investors react to news, prices may have already adjusted significantly. Additionally, the bid-ask spread can widen during volatile periods, potentially increasing the effective cost of buying or selling shares at that time.
What to Watch Next
Investors interested in how exchange mechanics play out in practice should watch how prices behave around the opening bell on days following significant overnight news, as this is often when the largest single adjustments occur. The formal signing of the US-Iran agreement later this week will provide another opportunity to observe how quickly and smoothly markets incorporate new information, particularly if the signing includes details that differ from current expectations. More broadly, monitoring how trading volumes and bid-ask spreads behave during periods of high versus low volatility can help investors better understand the practical functioning of the markets they invest in.
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Final Outlook
Stock exchanges function as continuous, automated marketplaces where prices reflect the real-time balance of buying and selling interest, a process that has become increasingly fast and algorithm-driven in 2026. The past 24 hours offered a clear, real-world example of this process in action, with a major overnight news event producing rapid, sector-specific price adjustments as markets opened and traded through the day. For Canadian investors, understanding these mechanics does not predict which direction prices will move, but it can help explain why markets move the way they do, and why the speed and sequencing of price adjustments matter as much as the underlying news itself.
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