German gas storage bookings for the current storage year have picked up in recent weeks, but large volumes of unbooked space combined with an unclear role of the state leave big question marks over the filling campaign this summer.
Germany started the storage year with at least 107TWh of unbooked storage capacity, out of a technical capacity of 247TWh (see data and download). An inverted THE summer 2025-winter 2025-26 spread through most of the winter created no incentive to book capacity.
But storage bookings have picked up in recent months, especially in May, with about 12.2TWh of storage space booked during the month, up from 5.5TWh in April and about 350GWh in March (see bookings graph). The THE summer 2025-winter 2025-26 spread has normalised since the beginning of April, which has re-established an incentive for traders to book storage space (see prices graph). In addition, the German government at the beginning of May lowered the legal 1 November fill level mandate to 80pc for most sites and 45pc for some slow-cycling aquifer sites and depleted fields. A lower stockfill mandate has contributed to the increased attractiveness of storage space, as it affords more flexibility to capacity holders.
What happens with unbooked capacity?
There remains at least 88.6TWh unbooked despite the uptick in bookings, and it remains unclear who would fill the space if it remains unsold.
The German gas storage act stipulates that German market area manager THE can book storage space if needed to fill gas storage sites to the legal level as a last resort. The Inzenham, Wolfersberg and Frankenthal sites remain completely unbooked so far, and THE may have to book some space to hit the 1 November target, according to current legislation.
THE has previously confirmed to Argus that it will only intervene at the point at which it is physically impossible for the market to fill the storage site on its own terms even if injecting at capacity.
In addition, THE may treat unbooked capacity at partially booked sites separately to allocated space. Most storage contracts pass on the storage targets to each capacity holder, suggesting that targets may still be missed at partially booked sites if firms only inject to the legal minimum. Remaining unbooked capacity at sites would then also have to be filled to 80pc or 45pc to ensure compliance with the site's target.
It is also unclear what injection capacity THE could make use of in the case of partially-booked sites, in order to fill unbooked space. If THE can take over all a site's injection capacity, it could start injecting considerably later than if it could only use the injection capacity proportionally allocated to the unbooked space. In the latter case, the market area manager would have to start intervening soon at some storage sites. At the 11.5TWh Breitbrunn site — a slow-cycling site with an 80pc target because of its location in Bavaria — THE might have to step in around mid-June to reach 80pc by 1 November for the 5.31TWh unbooked capacity, assuming an injection curve for the site in line with the German average as provided by Entsog. The site is currently filled to about 24pc of capacity, or 50pc of all booked capacity at the site, according to GIE transparency data.
The largest source of market uncertainty remains the 44.7TWh Rehden site, where only 894GWh is booked for the current storage year. The site now makes up about 50pc of unbooked storage space in Germany, and only 2pc of the site's capacity is allocated. THE would have to start filling the site in mid-August to reach the 45pc target, taking Rehden's specific injection curve and 18.5 days of maintenance in October into account.
But the German state has made a lot of noise recently that it does not want the market to rely on the state to fill storage this summer. But at the same time, THE's legal requirement to fill storage if market parties fail to do so remains intact, the market area manager confirmed to Argus recently.
Possible injections profiles point to remaining risk for 3Q tightness
Germany's cavern-heavy storage profile allows firms to delay a large part of storage injections far into the third quarter, especially if the market and state continue their "game of chicken" over unbooked capacity.
Germany needs to inject about 77.6TWh before 1 November to hit its target for every site, with five sites already above target, which would equate to a 500 GWh/d injection rate if spread evenly over the summer. The forward curve suggests an incentive to boost injections early in the summer, but it would be technically possible to delay 70TWh of injections until after 1 August and even 32.3TWh after 1 October, taking the Entsog average injection curve for each storage site (see theoretical injections profile graph). In that case, it would be theoretically possible for injection demand to peak at 2.6 TWh/d at the end of October. But 53.2TWh of the overall volume would have to be injected into unbooked capacity, if all capacity holders only fill to their mandated level.
Assuming that THE takes over injections for all unbooked capacity at each site and only has proportional injection capacity available, this would still result in backloaded injection demand. This would be concentrated in September and October, with THE-controlled injection demand peaking at about 900 GWh/d in late October (see THE injections profile graph).
Market participants have already warned of potential market tightness in late summer, given Norwegian maintenance scheduled during the period and possibly higher Asian cooling demand pulling LNG away from Europe. Delayed market-based injections, or any possible THE intervention, is likely to exacerbate this situation.
