[2] The popularity of the original Blackmar Gambit, however, was short lived, as it was basically unsound, allowing Black to secure a superior position after White's immediate 3.f3 with 3...e5!.

The evolved, modern form of this gambit owes much to the German master Emil Josef Diemer (1908–1990), who popularized the continuation 3.Nc3 Nf6 and then 4.f3 (when 4...e5?

The position resulting after 3... Nf6 4.f3 reflects the main line of the gambit accepted, although other Black responses on move three are possible.

After many years of analysis, Diemer wrote a book on the opening in the late 1950s, titled Vom Ersten Zug An Auf Matt!

), with most of the published analysis devoted to the Ryder Gambit (and associated Halosar Trap), a double-pawn sacrifice characterized by the moves 4...exf3 5.Qxf3.

[7] GM Boris Avrukh has written that the gambit "may not be fully correct" but cautioned that he "was surprised at just how potent White's initiative could become".

[8] GM Joe Gallagher wrote that he had "noticed a common trend among Blackmar–Diemer analysts; once there is no attack and the position looks rather balanced they tend to assess the game as =, forgetting the fact that they are a pawn down."

Gallagher thought that the closely related Hübsch Gambit gave an equal game but that the Blackmar–Diemer provided "not really enough compensation" and there were "a number of areas where Black could fight for the advantage."

"[10] IM Willy Hendriks notes that the main lines of the Blackmar–Diemer (1.d4 d5 2.e4 dxe4 3.Nc3 Nf6 4.f3 exf3 5.Nxf3) and the King's Gambit (1.e4 e5 2.f4 exf4 3.Nf3) have the same engine evaluation, and philosophically wonders whether the two might have swapped places in an alternative history.

[13] More common is 7...Bg6, which leads to quieter play, when White's best response is probably 8.Bg2 c6 9.h4, with a sustained kingside initiative in return for the pawn.

In this position, White can defend the attacked d-pawn with 8.Qf2 (the Ciesielski Variation), but this allows Black an easy game by preparing ...e7–e5, e.g. after 8...Nbd7 9.Bd3 e5.

?, the Seidel–Hall Attack, where White is happy to sacrifice the d-pawn in order to gain an increased initiative on the kingside, e.g. after 8...Qxd4 9.Be3 Qe5 10.0-0-0 e6 11.g5.

[20] The 5...e6 line, analysed by Max Euwe, aims to reach a French Defence type position, but with Black having an extra pawn.

Alternatively 7...Nc6 can be considered the main line of this variation, when 8.0-0 Nxd4 9.Kh1 is the notorious Zilbermints Gambit, sacrificing a second pawn in order to increase White's initiative.

White's most common response is the Studier Attack, 6.Bc4 Bg7 7.0-0 0-0 8.Qe1, intending Qh4, Bh6 and piling pressure on the kingside, sacrificing pawns at d4 and c2 if appropriate.

The best way to carry out this approach is via 6.Bf4, as 6.Bg5 (as played by Bogoljubov in his game against Diemer) is well met by 6...Bg7 7.Qd2 0-0 8.0-0-0 c5!, when Black stands better.

German FIDE master Stefan Bücker regards Black as clearly better after 10.Nf4 Bxf4 11.Bxf4 0-0,[31] but Christoph Scheerer believes that White can generate attacking chances with 12.c3 h6 13.Qg4!?.

[32] In view of White's problems proving compensation in these lines, ChessCafe.com reviewer Carsten Hansen concluded, "despite all the smoke and mirrors, the Blackmar–Diemer Gambit still isn't viable beyond club-level or rapid-play games".

[34] Black cannot easily deviate from this line, since after 7...Nbd7 White continues 8.Qe2 e6 9.0-0-0, aiming to launch a strong attack down the e- and f-files, and if 9...Bb4 then 10.d5!.

The line continues 8...Na6 9.Qxb7 Qe4 (Black lost in Diemer vs. Halosar, Baden-Baden 1934, after 9...Rc8 10.Qxa6) 10.Qxa6 Qxe3+ (worse is 10...Bxd1 11.Kxd1 Rd8+ 12.Bd2 and White is winning, for example 12...Ng4 13.Nxc7+ Kd7 14.Qxa7) 11.Kb1 Qc5 12 Nf3.

Alternatively, 5.Nxe4 is likely to land White in an inferior version of the Fantasy Variation of the Caro–Kann Defence, with equality at best in positions that may not attract Blackmar–Diemer players, 5.fxe4 e5!

[40] The Vienna Defence was recommended by Matthias Wahls in his book Modernes Skandinavisch, where he saw it as a refutation of the Blackmar–Diemer Gambit.

In most lines White must seek to place a knight on f4 (taking the sting out of ...Nd5) in order to secure an advantage.

[46] Since these positions typically do not attract gambiteers, White often chooses a riskier response in order to generate winning chances, such as 4.Qh5, 4.Nge2 or 4.Nxe4.

[50][51] Gary Danelishen, author of The Final Theory of Chess, posted analysis of the Torning Variation online.