A double logarithmic plot of a resistivity measurement on the x-axis versus a porosity measurement on the y-axis. The plot is named after G.R. Pickett. The plot is based on taking the logarithm of the Archie equation. Points of constant water saturation (S_{w}) will plot on a straight line with negative slope of value m. Water zones define the lowermost line on the plot. Since S_{w} = 1, the water resistivity can be determined from a point on the line. Once the water line is established, other parallel lines can be drawn for different S_{w}, assuming a constant n (usually 2). Other data can then be plotted and interpreted in terms of S_{w}. The same technique can be applied to the flushed zone, using flushed-zone measurements.
See Pickett GR: "A Review of Current Techniques for Determination of Water Saturation from Logs," paper SPE 1446, presented at the SPE Rocky Mountain Regional Meeting, Denver, Colorado, USA, May 23-24, 1966; SPE Journal of Petroleum Technology (November 1966): 1425-1435.