Reading the BSE chain, and how it differs from NSE
SENSEX and BANKEX options work the same way NIFTY and BANK NIFTY options do. The differences are in liquidity and expiry scheduling, and both of them matter more than the similarity does.
Liquidity is the first thing to check
BSE's derivatives volumes are a fraction of NSE's, and the gap is not evenly spread. At-the-money strikes on SENSEX in the current weekly expiry trade reasonably; move two or three strikes out, or into a later expiry, and the bid-ask spread widens fast.
That spread is a real cost paid at entry and again at exit, and on a wide one it can exceed the move you were trading for. Before taking a level from this chain seriously, look at what it would cost to get in and out of it. A strike with heavy open interest and no depth is a statistic, not a tradeable level.
Expiry days are not the same
SENSEX and BANKEX weekly contracts settle on their own schedule, separate from NIFTY's and BANK NIFTY's. This is the source of most of the confusion around these contracts, and it has a practical consequence: on a day when a BSE contract is expiring and the NSE ones are not, BSE index options behave like expiry-day instruments — gamma high, theta brutal, premiums decaying in minutes — while the NSE chain next to them looks placid.
Check which contract you are actually looking at before reading anything into a premium that seems mispriced. It usually isn't.
What is still worth watching here
SENSEX and NIFTY track each other closely — they overlap heavily in constituents — so the two chains usually agree, and the interesting information is in the moments they don't. A PCR or a buildup bias that diverges between the two exchanges is generally a liquidity artefact rather than a signal, and the NSE reading is the one to trust when they disagree.
BANKEX against BANK NIFTY is the more informative pair, because banking is where index-level divergence tends to show up first. Both are on this site; the NSE side is on the main option chain.