For fans of beloved but low-rated television series, this can be a nerve-wracking time of year.

With the current television season coming to a close, executives at the major TV networks will soon be looking to solidify their fall lineups, which have not yet been officially decided upon.

For many shows that post decent but unexceptional ratings, this means the threat of cancellation. These shows, left in limbo as to their future, are said to be “on the bubble.”

According to an article in USA Today, this year’s crop of bubble shows includes many previously popular series.

On ABC, a large number of new programs make up the bubble category, including “Samantha Who?,” “Cupid” and “Castle.” Already long gone are former powerhouse “Boston Legal” and the critically-acclaimed “Life on Mars.” Popular shows “Lost,” “Desperate Housewives” and “Grey’s Anatomy” are all safe on the schedule for at least another year.

Over on CBS, a strong lineup across the board has put decently performing procedural shows such as “Cold Case,” “Without a Trace” and “The Unit” into bubble show status, with only the dreadfully rated “The Ex-List” a lock for cancellation. On the flip side, popular shows “How I Met Your Mother,” “The Mentalist” and “CSI: Crime Scene Investigation” are all safe.

For NBC, the arrival of the new “The Tonight Show with Jay Leno” time slot at 10 p.m. means an even tighter schedule than before, pushing low-rated shows “Kath & Kim” and “Kings” off the air, and others like “Chuck,” “My Name is Earl” and “Medium” into bubble territory. In no danger, however, are wildly popular shows “The Office,” “30 Rock” and usual bubble entry “Friday Night Lights,” all of which have been guaranteed a place on the fall schedule.

On Fox, Joss Whedon’s “Dollhouse” and the new animated show “Sit Down, Shut Up” are the only programs considered to be on the bubble, whereas “Prison Break,” “Terminator: The Sarah Connor Chronicles” and “King of the Hill” are likely gone for good. Old favorites “The Simpsons,” “Family Guy,” “House” and “24” are all in locks to return.

Finally, things are relatively stable on The CW, with only “Privileged” and “Everybody Hates Chris” still uncertain as to their fates. This leaves the possibility that the CW will run its fall schedule without a single comedic entry. Poorly rated shows “Reaper” and “Valentine” are gone, while favorites “Gossip Girl,” “90210,” “One Tree Hill” and the long-running “Smallville” will all return.

For each of these bubble shows, the threat of cancellation looms large. Given the realities of television, some of them will certainly be canceled, much to the chagrin of fans. However, in the modern television industry, even cancellation isn’t necessarily the end with life in other mediums, including DVDs, motion pictures and even comic books.