Some general notes on the Stalingrad airlift:

AGS, and in particular 6th Army, had been getting a portion of its daily supply requirement by air prior to the encirclement. This was due to the lack of a rail line (as noted previously, the single rail line available ended at Stalino about 400 km to the rear of the German advance at Stalingrad) and the shortage of motor vehicles to haul supplies forward.
Initially, the Germans alloted approxmately 11,000 trucks in general headquarters units to lift supplies for the offensive. This was done in part by stripping the civilian economy in occupied areas and by stripping most divisions not in the assault of all or most of their motor transport. Of course, after weeks of use many of these trucks were no longer runners most having already seen extensive use before this point in the war.
Up through the encirclement of 6th Army the Luftwaffe had flown in 9,223 tons of supplies and had also had to airlift a good portion of their own supply needs in addition to that.

As for aircraft committed, the first week saw only a handful of locally available aircraft in use. Sorties per day hovered around 30 or so in this period.
By December 5 (about 10 days after the operation started) there were 11 Gruppen of Ju 52, 2 more formed with Ju 86 from bomber schools manned by the instructors, and four of He 111.
As the airlift progressed, the Henkel proponet grew to 14 Gruppen basically stripping the Luftwaffe of any offensive capacity it might have had. In addition, aircraft from Fleiger Führer Atlantic were flown in (primarily Fw 200s) along with the prototype Ju 290 and several He 177. The total aircraft on hand quickly reached over 600 with about a 20% operational rate on any given day.
On January 13 for example, there were 317 Ju 52, 181 He 111, 20 Fw 200, 1 Ju 290, and 10 He 177 available for the airlift. In addition 87 Ju 52 and 219 He 111 were enroute from other portions of the Reich to augment this lift.
Of the above, only 47 aircraft were deemed operational and these managed 69 sorties delivering 224.5 tons of supplies. In all, this was one of the better days of the airlift.