Source: Defending a Conventional 3NT Opening The gambling 3NT opening is a popular method in US Tournament bridge. An opening 3NT promises a solid 7-card minor with no outside high cards. Personally, I don’t care for this method, but I must be prepared to bid against it, since it is quite common. At the four level, bidding options are severely constrained. Any method we adopt–even natural bidding–involves tradeoffs. For example, suppose we use natural bidding over a 3NT opening. We are well placed when we hold single-suited hands like:
• AKxxxxx, Axx, x, xx
• KQT9xx, xx, AKxx, x
We are less well placed when we hold a 2-suiter.
• AKQxx, QTxxx, Ax, x
• Kxxxx, x, AKJxxx, x
We must pick the battles we want to win. The most important battles are those where we can make four of a major because they will be our most common games.* We’d like to differentiate one-suited from two-suited hands with a major. Here is my suggestion: (3NT) — ? 4 = both majors 4 = One major 6+ 4M = 5-card major and a 5+ card minor 4NT = Slam-interested hand with a long minor (Ax, QJx, AKQxxxxx, –) 5m = To play, with a long minor This method trades the ability to overcall a natural 4m to gain the ability to show 2-suited hands that include a major. When overcaller has both majors, the partnership can reliably get to the best major game. For example: (3NT) — 4 — (P) — ? 4 = pick your best major 4M = My longest major When overcaller has a major and a minor, the partnership can get to 4M when it is right without risking a disaster when  advancer does not fit the major: (3NT) — 4 — (P) — ? 4 = to play 4NT = RKC 5 = pass or correct A hand like this is a nightmare using natural overcalls. Kxxxx, x, AKJxxx, x. If you overcall 4, you may miss a good 4 spades, but if you bid 4S, you may go down 4 when 5 was cold. Using my method, this hand is easily handled. Other Opportunities The same method can be used without any changes in two other situations:
• 3NT opening showing a long broken minor. If your opponents play the Namyats convention, where 3NT promises a 4m preempt the same defense works well.
• (1NT) — P — (3NT) — ? You wont want to bid very often in this auction, but when you want to sacrifice over 3NT, you are more likely to hold one or both majors than a minor.
————– * 5 of a minor will be rare since only one minor is available and that contract requires us to take 11 tricks instead of 10.