下列兩種情況表明交易活動的不尋常：1、交易量高於平常表明交易興趣濃厚；2、交易量也可以低於平常水平，顯示交易興趣匮乏。這兩種情況對於推測價格走勢都很重要。
識別不同尋常的交易量
交易日志的讀者或許會發現，我經常用到比爾麥克拉倫的方法來快速識別不尋常的交易量。
交易量圖表上的兩條水平線把交易量劃分成了三類：
a.交易量突破上面的一條線：不同尋常的高交易量；
b.交易量位於兩條線之間：尋常交易量（大部分的k線可以被忽略，但是要留意趨勢的變化：維持一週或更長時間的交易量減少或增加。）
c.交易量位於下面一條線的下方：不尋常的低成交量（成交量枯竭）。
交易量橫線的畫法：
• 根據去年的交易量來設置這兩條橫線；
• 確保上面的一條線上方能顯示出每季度的高交易量；
• 同樣，下面的一條直線也要突出每個季度的低交易量；
• 過多的交易信號會削減這兩條線的有效性，可以將上方的一條線設置為40或50。
如果我將上方的橫線設置在1.5百萬成交量，那麼我將錯失很多有用的交易信號。
註意：
• 偶爾的高成交量是某個大機構的交易引起的，該機構的購買決定或許是幾週之前就已經被商讨，與圖表上的高交易量沒有必然聯系。如果成交量達到日常均值的5~10倍，不論是否由某一機構引起，你都應該進場；
• 不要被聖誕節、複活節或者週末到來之前的低交易量所迷惑；
• 小心對待指數、股票等結算日引起的交易量升高。
交易信號
高價格和高交易量
在一個強勁的上升趨勢中，高價格和大成交量通常或引起反轉：在過度超買或超賣的情況下，市場專業人士會逆趨勢交易。
上升趨勢：上圖中顯示的是上升趨勢的衰竭狀態。價格長期呈現上升走勢，並在[1]處快速上升。接下來的k線走出了長影線，交易量也隨之升高，預示著獲利退場。[6]處價格範圍波動大，交易量進一步升高。[7]處是典型的衰竭缺口，日交易量也隨著達到了1千萬。接下來的4天股票價格幾乎下降了40%。[12]處的小陽線和高交易量預示一輪反轉，但是買方已近衰竭，上升幅度有限。接下來一輪下降趨勢開始。
下降趨勢：[1]處恐慌性的抛售表明價格被賣方控制。[2]處的成交量巨大表明買賣雙方勢均力敵，進而形成了支撐位。
窄幅震蕩（買賣雙方勢均力敵）期間的交易量升高通常會使價格突破震蕩區間並沿襲原來走勢，常會伴隨著長尾線的蠟燭圖。
加德士澳大利亞石油股價在8.5~10區間震蕩長達6個月，突破之前出現了兩個典型的買入信號：[1]處在震蕩區間的下方出現空頭陷阱；[2]處阻力位的貝殼狀回調，交易量也顯著增加。
下面的等量成交圖通過寬度展現交易量，開盤價、收盤價描述方法與蠟燭圖類似。
[a]處在價格達到阻力位10.00出現一大波獲利回吐，[c]處價格穿透支撐位，導致一輪抛售。[d]處狹窄的交易範圍和高交易量提醒我們買方仍然強勢，並全部吸收了之前獲利回吐的賣單。[e]處交易量進一步擴大，但是主體部分狹窄，代表著一根十字星線。[f]處賣方壓力減少，並在[g]處枯竭。說明新一輪的上漲即將到來。
交易量衰竭
上圖股價的小幅扇貝形態回調是上升趨勢中的牛市信號，或下降趨勢中的熊市信號。它的價格波動範圍小，交易量低，表明賣方（買方）壓力減少。
趨勢的迅速反轉同樣也是進場的信號，前提是該反轉持續時間短並帶有長長的尾線，或者是伴隨著交易量的升高。
交易量迅速升高產生的缺口同樣也是主要的交易信號。比如上圖中[7]處的衰竭缺口和下面我們講述的兩個實例。
1. [1]處一個巨大的衰竭缺口伴隨著高成交量說明買方放棄希望；
2. 接下來的一天，市場專業人士在意識到該股票的真正價值之後以低價買入股票；
3. 三個月後，價格再次走低並試探4.00的支撐位。在[3]處缺口伴隨高交易量形成之前，價格實際上已經穿透了支撐位。牛市在價格於[3]處突破下降趨勢線的時候顯現出來。上述例子中，價格同樣也跳過了支撐/阻力位，進一步加強此時的牛市信號；
4. [4]處小幅回調和低交易量表明下降趨勢枯竭。
Volume Spikes and Dips
There are two times where daily volume will highlight unusual trading activity:
1. Volume may spike above the normal range, signaling unusual trading interest; and
2. Volume may also dip below the normal range, indicating a lack of trading interest.
Both of these signals are important and can forewarn of future price movement.
Identifying Unusual Volume
Readers of the Trading Diary will notice that I frequently use a method, learned from Bill McLaren, to quickly identify unusual volume.
Two horizontal lines are visually fitted over Volume, separating volume bars into three categories:
• above the top line = unusual activity
• between the lines = normal activity (daily bars can be largely ignored but one should still watch for trends: increasing or decreasing volume over a week or more)
• below the bottom line = unusually low activity (where volume has dried up)
Hints
• Fit the lines based on the last year's volume and extend them forward each week when you review the chart;
• Ensure that the top line will highlight at least one volume bar in each quarter;
• Likewise with the bottom line;
• Too many signals on the other hand will negate their usefulness - set an upper limit of 40 or 50.
I would have missed a number of decent signals, in April/May on the above chart, if I had raised the upper line to 1.5 million.
Cautions
• Occasionally volume spikes are the result of a single large institutional transaction. The actual deal may have been negotiated over several weeks and has little relevance to the course of sales on the day on which it is booked. If volume is 5 or 10 times the daily average, you need to establish whether it was caused by a single transaction.
• Be careful not to confuse low trading volume with the lull in activity generally experienced over Christmas, Easter and prior to most long weekends.
• Volume spikes on triple-witching days (especially on indexes and major stocks) should be treated with caution.
Trading Signals
Price and Volume Spike
In a strong established trend, large price and volume spikes often precede a major reversal: the security has either been substantially overbought or oversold and market professionals step in and buy/sell against the trend.
Up-Trend
The Charles Schwab chart (above) shows a classic blow-off pattern in an up-trend. The long-established trend started to accelerate at [1]. Day [2] displays a tall shadow and huge volume, signaling profit-taking. A wide-ranging day at [6] leaves a tall blue candle with even higher volume -- a typical blow-off signal. The gap on day [7] is another classic blow-off sign -- see exhaustion gaps. Daily volume now approaches a massive 10 million as the big money steps in, selling the stock down almost 40% over the next 4 days. A narrower blue candle and strong volume at [12] signal the start of a rally but buying demand has been absorbed and the rally fizzles out, commencing a primary down-trend.
Down-Trend
In a strong down-trend, a wide ranging day [1] accompanied by a volume spike signals the transfer of large amounts of stock from weak to strong hands, establishing a strong support level. Australian ear implant specialist Cochlear fell sharply in 2002 before forming a broad base in 2003 until a fall below the $30 support level eventually triggered panic selling (the "abandonment of all hope" mentioned by Charles Dow). The stock fell sharply on day [1] on huge volume. Compare the trading range to day [2] which showed even higher volume as large buyers, perceiving real value, started buying against the trend, establishing a strong support level at $20.
Trading Range
In a trading range, large volumes on a wide-ranging day will signal the likely direction of a breakout.
Compressed Spring
In a reaction during a trend, a volume spike combined with a narrow trading range often precedes a big move in the direction of the trend; committed opposition (to the reaction) having compressed the trading range.
A similar (though weaker) signal is offered by a volume spike accompanied by a candle with a long tail.
Caltex Australia consolidated in a band between 8.50 and 10.00 for about 6 months, following a strong up-trend, before exhibiting two classic buy signals:
• a bear trap [1] at the lower border of the consolidation; followed by
• a small scallop below resistance at [2].
What is remarkable is the volume on the scallop at [2]. The equivolume chart below depicts volume by the width of the bars (open and close are reflected in a similar manner to candlesticks).
Profit-taking is evident at [a] as price again approaches resistance at 10.00. Price penetrates resistance at [c], triggering committed selling. The narrow range and huge volume at [d] alert us to the presence of strong buying, absorbing all stock that profit-takers offer in the market. Day [e] is looser, with a wider range but narrow body resembling a doji candle, on even larger volume. Selling pressure abates somewhat at [f] before a complete dry-up of trading activity at [g] signals that sellers are exhausted and a rally is imminent.
Trading Dries Up
A shallow correction/reaction in the form of a scallop, such as the one on the above Caltex Australia chart, is a bullish sign in an up-trend (or bearish in a down-trend). The best signal that the primary trend movement is about to resume is a narrow ranging day on unusually low volume, indicating that selling (or buying) pressure has abated.
This page has two examples:
• at [g] in the Caltex equivolume chart above; and
• at [4] in the Brambles chart below.
Reactions
A sharper reaction against the trend can still offer good buy signals (or sell signals in a down-trend), provided that the reaction is of short duration and ends with a long tail or reversal signal accompanied by a volume spike.
Gaps
Gaps accompanied by a volume spike often provide major signals. Earlier we saw a prominent exhaustion gap [7] during a blow-off on the Charles Schwab chart. The Brambles chart below provides two excellent examples:
• an exhaustion gap during a cathartic sell-off at [1]; and
• a breakaway gap accompanied by another volume spike at [3].
1. The large downward exhaustion gap is accompanied by massive volume as sellers abandon hope.
2. By the next day market professionals, having spotted real value, are buying in the face of the down-trend, mopping up all available stock at keen prices.
3. Three months later price again tests $4.00 after drifting lower. The stock actually penetrates the support level before gapping upwards accompanied by a volume spike at [3]. Sometimes referred to as a hole-in-the-wall gap, a strong bull signal is made when price gaps to above a downward trendline. In the above case, price also gaps above the support/resistance, adding extra weight to the signal.
4. Volume and trading range dry up on a shallow retracement.
Breakouts
A volume spike immediately after a breakout signals a healthy trend. Absence of volume signals weakness.
本文翻譯由兄弟財經提供
本文來源：http://www.incrediblecharts.com/technical/volume_spikes.php