Page 513: The notation used in the equation for St at the foot of the right-hand side main column on page 513 is at least confusing, and strictly speaking incorrect. The upper limit of integration (time t) uses the same notation as the indicator defining the integration operator itself (also t). Although the meaning of the equation is probably understood by readers, it is preferable to use the notation employed previously in Equation 14.9 on page 481 (although in Chapter 15 S bar is used to denote the initial, period zero, stock, while S0 was used for the same quantity in Chapter 14).

Page 522: The notation used for the P value in the upper left-side quadrant of Figure 15.9 is incorrect in one place. The lower of the two P values should not have the ' symbol attached as a superscript.

Page 523: Figure 15.10, lower left-side quadrant. There is a mistake in the way in which the dotted line connecting the R axis to the time axis has been drawn, and a lack of clarity of exposition in the diagram and in its associated text. A revised diagram has been placed in the pages giving images for the textbook.

Note first that for both scenarios being discussed in this example - with the initial, high choke price, and with the second, lower choke price, a rational plan will draw down the remaining stock to zero at exactly the point in time where the net price reaches the choke price. This does not, of course, mean that the extraction rate, R, has to be near to zero at points in time just prior to the swithch to the backstop. But nevertheless, the total amount extracted must be identical in the two cases. This is not what the dotted line in the lower left-side quadrant shows in the text as it is currently drawn.

The dotted line corresponding to the extraction quantity over time to the time of exhaustion under the new lower choke price scenario needs to have the following properties. First, it will be a negatively sloping line as shown from t = 0 onwards until t = T' . Also, it will lie below the continuous, downward sloping line, as with a lower price the extraction rate will be higher. After t = T' is reached, there is a discontinuity: the extraction rate, R, jumps from the level it was immediately prior to T' to zero. (In the revised diagrams, this extraction rate is indicated as R*.) This is shown as a horizontal section of the dotted line in Figure 15.10, but should be interpreted with caution as there is actually a discontinous jump from a positive extraction rate (R*) to zero extraction rate at T'.

When correctly drawn there will be two triangles on the diagram that are the same in area. The first of these (shown in Figure 15.10a) in the revised file, and indicated in green shading, is the one that is currently shaded in grey in the textbook. The second - shaded in yellow in Figure 15.10b) is another triangle, not currently shown in the textbook. It is formed as the triangle lying between the R axis itself, a vertical line dropped down from the R axis at the resource extraction rate that exists immediately before the choke price is reached (R*), and the downward sloping section of the correctly drawn dotted line. The correctly drawn diagram should be one in which these two areas (the green and the yellow triangular areas) are of equal magnitude. That is approximately so in my redrawn diagram.

Thanks to Krister Hjalte for alerting me to these mistakes.