December desktop search rankings from comScore came out yesterday. Bing gained slightly versus November; most others are off a fraction of a point.

Google has lost market share and volume versus a year ago, when it had a share of 65.4 percent. A year ago, Bing was at 19.7 percent; today it’s at 21.1 percent. However, these data tell only part of the story because they don’t include mobile search.

ComScore says that in terms of total market share, including “powered by” search, Google controlled 64.8 percent of US search query volume, while Bing powered 32.2 percent of organic search.

Data below show that month-over-month desktop search volume is flat. Compared with a year ago, PC queries were down by 1.2 billion overall. That’s mostly attributable to a decline in queries on Google, which may have transferred to mobile.

As indicated, the charts and data above don’t reflect mobile search volumes, which are probably relatively modest for Bing and Yahoo but quite significant for Google. The company said last year that mobile queries surpassed PC search volumes in numerous countries, including the US.

Accordingly, we can assert with some confidence — assuming the comScore estimates above are correct — that Google’s total search volume is at least 2X the numbers reflected in the chart above. As I’ve argued in the past, comScore should now be providing the market with a combined view of mobile and PC search volumes.

By looking only at PC data, we get a distorted view of the actual state of the US search market.